diff --git a/src/compiler/abepi.rs b/src/compiler/abepi.rs
index ceac8789..03b488ff 100644
--- a/src/compiler/abepi.rs
+++ b/src/compiler/abepi.rs
@@ -65,6 +65,9 @@ impl<F: From<u64> + TryInto<u32> + Clone + Debug, V: Clone + Debug> CompilationU
             Statement::Transition(dsym, id, stmt) => {
                 self.compiler_statement_transition(dsym, id, *stmt)
             }
+            Statement::HyperTransition(dsym, ids, call, state) => {
+                self.compiler_statement_hyper_transition(dsym, ids, call, state)
+            }
             _ => vec![],
         }
     }
@@ -420,6 +423,16 @@ impl<F: From<u64> + TryInto<u32> + Clone + Debug, V: Clone + Debug> CompilationU
 
         result
     }
+
+    fn compiler_statement_hyper_transition(
+        &self,
+        _dsym: DebugSymRef,
+        _ids: Vec<V>,
+        _call: Expression<F, V>,
+        _state: V,
+    ) -> Vec<CompilationResult<F, V>> {
+        todo!("Compile expressions? Needs specs")
+    }
 }
 
 fn flatten_bin_op<F: Clone, V: Clone>(
diff --git a/src/compiler/compiler.rs b/src/compiler/compiler.rs
index 9a3c5584..e717a993 100644
--- a/src/compiler/compiler.rs
+++ b/src/compiler/compiler.rs
@@ -558,57 +558,22 @@ mod test {
 
     use crate::{
         compiler::{compile, compile_file, compile_legacy},
-        parser::ast::debug_sym_factory::DebugSymRefFactory,
+        parser::{ast::debug_sym_factory::DebugSymRefFactory, lang::TLDeclsParser},
         wit_gen::TraceGenerator,
     };
 
     use super::Config;
 
-    // TODO rewrite the test after machines are able to call other machines
+    // TODO improve the test for HyperTransition
     #[test]
     fn test_compiler_fibo_multiple_machines() {
         // Source code containing two machines
         let circuit = "
-        machine fibo1 (signal n) (signal b: field) {
-            // n and be are created automatically as shared
-            // signals
-            signal a: field, i;
-
-            // there is always a state called initial
-            // input signals get bound to the signal
-            // in the initial state (first instance)
-            state initial {
-             signal c;
-
-             i, a, b, c <== 1, 1, 1, 2;
-
-             -> middle {
-              i', a', b', n' <== i + 1, b, c, n;
-             }
-            }
-
-            state middle {
-             signal c;
-
-             c <== a + b;
-
-             if i + 1 == n {
-              -> final {
-               i', b', n' <== i + 1, c, n;
-              }
-             } else {
-              -> middle {
-               i', a', b', n' <== i + 1, b, c, n;
-              }
-             }
-            }
-
-            // There is always a state called final.
-            // Output signals get automatically bound to the signals
-            // with the same name in the final step (last instance).
-            // This state can be implicit if there are no constraints in it.
+        machine caller (signal n) (signal b: field) {
+            signal b_1: field;
+            b_1' <== fibo(n) -> final;
            }
-           machine fibo2 (signal n) (signal b: field) {
+           machine fibo (signal n) (signal b: field) {
             // n and be are created automatically as shared
             // signals
             signal a: field, i;
@@ -839,4 +804,43 @@ mod test {
             r#"[SemErr { msg: "use of undeclared variable c", dsym: test/circuit_error.chiquito:24:39 }, SemErr { msg: "use of undeclared variable c", dsym: test/circuit_error.chiquito:28:46 }]"#
         )
     }
+
+    #[test]
+    fn test_parse_hyper_transition() {
+        let circuit = "
+        machine caller (signal n) (signal b: field) {
+            a', b, c' <== fibo(d, e, f + g) -> final;
+        }
+        ";
+
+        let debug_sym_ref_factory = DebugSymRefFactory::new("", circuit);
+        let result = TLDeclsParser::new().parse(&debug_sym_ref_factory, circuit);
+
+        assert!(result.is_ok());
+
+        let circuit = "
+        machine caller (signal n) (signal b: field) {
+            -> final {
+                a', b, c' <== fibo(d, e, f + g);
+            }
+        }
+        ";
+
+        let debug_sym_ref_factory = DebugSymRefFactory::new("", circuit);
+        let result = TLDeclsParser::new().parse(&debug_sym_ref_factory, circuit);
+
+        assert!(result.is_ok());
+
+        // TODO should no-arg calls be allowed? Needs more specs for function/machine calls
+        let circuit = "
+        machine caller (signal n) (signal b: field) {
+            smth <== a() -> final;
+        }
+        ";
+
+        let debug_sym_ref_factory = DebugSymRefFactory::new("", circuit);
+        let result = TLDeclsParser::new().parse(&debug_sym_ref_factory, circuit);
+
+        assert!(result.is_ok());
+    }
 }
diff --git a/src/compiler/semantic/analyser.rs b/src/compiler/semantic/analyser.rs
index 3664608d..e5291ea4 100644
--- a/src/compiler/semantic/analyser.rs
+++ b/src/compiler/semantic/analyser.rs
@@ -272,6 +272,11 @@ impl Analyser {
 
             Statement::SignalDecl(_, _) => {}
             Statement::WGVarDecl(_, _) => {}
+            Statement::HyperTransition(_, ids, call, state) => {
+                self.analyse_expression(call);
+                self.collect_id_usages(&[state]);
+                self.collect_id_usages(&ids);
+            }
         }
     }
 
@@ -308,6 +313,12 @@ impl Analyser {
             } => {
                 self.extract_usages_expression(&sub);
             }
+            Expression::Call(_, fun, exprs) => {
+                self.collect_id_usages(&[fun]);
+                exprs
+                    .into_iter()
+                    .for_each(|expr| self.extract_usages_expression(&expr));
+            }
             _ => {}
         }
     }
diff --git a/src/compiler/semantic/rules.rs b/src/compiler/semantic/rules.rs
index 5bf846e8..818162c1 100644
--- a/src/compiler/semantic/rules.rs
+++ b/src/compiler/semantic/rules.rs
@@ -43,6 +43,9 @@ fn undeclared_rule(analyser: &mut Analyser, expr: &Expression<BigInt, Identifier
             undeclared_rule(analyser, when_false);
         }
         Expression::Const(_, _) | Expression::True(_) | Expression::False(_) => {}
+        Expression::Call(_, _, args) => {
+            args.iter().for_each(|arg| undeclared_rule(analyser, arg));
+        }
     }
 }
 
diff --git a/src/compiler/setup_inter.rs b/src/compiler/setup_inter.rs
index 9b2b3e24..30130eaa 100644
--- a/src/compiler/setup_inter.rs
+++ b/src/compiler/setup_inter.rs
@@ -250,6 +250,7 @@ impl SetupInterpreter {
 
             SignalAssignment(_, _, _) | WGAssignment(_, _, _) => vec![],
             SignalDecl(_, _) | WGVarDecl(_, _) => vec![],
+            HyperTransition(_, _, _, _) => todo!("Implement compilation for hyper transitions"),
         };
 
         self.add_poly_constraints(result.into_iter().map(|cr| cr.anti_booly).collect());
diff --git a/src/interpreter/expr.rs b/src/interpreter/expr.rs
index afc85830..d0eb3f9b 100644
--- a/src/interpreter/expr.rs
+++ b/src/interpreter/expr.rs
@@ -82,6 +82,9 @@ pub(crate) fn eval_expr<F: Field + Hash, V: Identifiable>(
         Const(_, v) => Ok(Value::Field(F::from_big_int(v))),
         True(_) => Ok(Value::Bool(true)),
         False(_) => Ok(Value::Bool(false)),
+        Call(_, _, _) => {
+            todo!("Needs specs. Evaluate the argument expressions, evaluate the function output?")
+        }
     }
     .map_err(|msg| Message::RuntimeErr {
         msg,
diff --git a/src/interpreter/mod.rs b/src/interpreter/mod.rs
index 7cd05010..fc71787c 100644
--- a/src/interpreter/mod.rs
+++ b/src/interpreter/mod.rs
@@ -206,6 +206,7 @@ impl<'a, F: Field + Hash> Interpreter<'a, F> {
             Block(_, stmts) => self.exec_step_block(stmts),
             Assert(_, _) => Ok(None),
             StateDecl(_, _, _) => Ok(None),
+            HyperTransition(_, _, _, _) => todo!("Needs specs"),
         }
     }
 
diff --git a/src/parser/ast/expression.rs b/src/parser/ast/expression.rs
index 61556d11..941641ad 100644
--- a/src/parser/ast/expression.rs
+++ b/src/parser/ast/expression.rs
@@ -193,6 +193,12 @@ pub enum Expression<F, V> {
     Const(DebugSymRef, F),
     True(DebugSymRef),
     False(DebugSymRef),
+    /// Function or machine call.
+    /// Tuple values:
+    /// - debug symbol reference;
+    /// - function/machine ID;
+    /// - call argument expressions vector.
+    Call(DebugSymRef, V, Vec<Expression<F, V>>),
 }
 
 // Shorthand for BigInt expression
@@ -217,6 +223,9 @@ impl<F, V> Expression<F, V> {
             Const(_, _) => true,
             True(_) => false,
             False(_) => false,
+            Call(_, _, _) => {
+                todo!("Needs specs. For a function call, depends on the function return type?")
+            }
         }
     }
 
@@ -234,6 +243,9 @@ impl<F, V> Expression<F, V> {
 
                 when_true.is_logic()
             }
+            Expression::Call { .. } => {
+                todo!("Needs specs. For a function call, depends on the function return type?")
+            }
             _ => false,
         }
     }
@@ -247,6 +259,7 @@ impl<F, V> Expression<F, V> {
             Expression::Const(dsym, _) => dsym,
             Expression::True(dsym) => dsym,
             Expression::False(dsym) => dsym,
+            Expression::Call(dsym, _, _) => dsym,
         }
     }
 
@@ -260,6 +273,7 @@ impl<F, V> Expression<F, V> {
             Expression::Query(_, _) => false,
             Expression::True(_) => false,
             Expression::False(_) => false,
+            Expression::Call(_, _, _) => false,
         }
     }
 }
@@ -315,6 +329,7 @@ impl<F: Debug, V: Debug> Debug for Expression<F, V> {
 
             Expression::True(_) => write!(f, "true"),
             Expression::False(_) => write!(f, "false"),
+            Expression::Call(_, fun, exprs) => write!(f, "{:?}({:?})", fun, exprs),
         }
     }
 }
diff --git a/src/parser/ast/statement.rs b/src/parser/ast/statement.rs
index 1d7e9b7f..896cd50e 100644
--- a/src/parser/ast/statement.rs
+++ b/src/parser/ast/statement.rs
@@ -13,28 +13,42 @@ pub struct TypedIdDecl<V> {
 
 #[derive(Clone)]
 pub enum Statement<F, V> {
-    Assert(DebugSymRef, Expression<F, V>), // assert x;
-
-    SignalAssignment(DebugSymRef, Vec<V>, Vec<Expression<F, V>>), // x <-- y;
-    SignalAssignmentAssert(DebugSymRef, Vec<V>, Vec<Expression<F, V>>), // x <== y;
-    WGAssignment(DebugSymRef, Vec<V>, Vec<Expression<F, V>>),     // x = y;
-
-    IfThen(DebugSymRef, Box<Expression<F, V>>, Box<Statement<F, V>>), // if x { y }
+    /// assert x;
+    Assert(DebugSymRef, Expression<F, V>),
+    /// x <-- y;
+    SignalAssignment(DebugSymRef, Vec<V>, Vec<Expression<F, V>>),
+    /// x <== y;
+    SignalAssignmentAssert(DebugSymRef, Vec<V>, Vec<Expression<F, V>>),
+    /// x = y;
+    WGAssignment(DebugSymRef, Vec<V>, Vec<Expression<F, V>>),
+    /// if x { y }
+    IfThen(DebugSymRef, Box<Expression<F, V>>, Box<Statement<F, V>>),
+    /// if x { y } else { z }
     IfThenElse(
         DebugSymRef,
         Box<Expression<F, V>>,
         Box<Statement<F, V>>,
         Box<Statement<F, V>>,
-    ), // if x { y } else { z }
-
-    SignalDecl(DebugSymRef, Vec<TypedIdDecl<V>>), // signal x;
-    WGVarDecl(DebugSymRef, Vec<TypedIdDecl<V>>),  // var x;
-
-    StateDecl(DebugSymRef, V, Box<Statement<F, V>>), // state x { y }
-
-    Transition(DebugSymRef, V, Box<Statement<F, V>>), // -> x { y }
-
-    Block(DebugSymRef, Vec<Statement<F, V>>), // { x }
+    ),
+    /// signal x;
+    SignalDecl(DebugSymRef, Vec<TypedIdDecl<V>>),
+    /// var x;
+    WGVarDecl(DebugSymRef, Vec<TypedIdDecl<V>>),
+    /// state x { y }
+    StateDecl(DebugSymRef, V, Box<Statement<F, V>>),
+    /// Transition to another state.
+    /// -> x { y }
+    Transition(DebugSymRef, V, Box<Statement<F, V>>),
+    /// { x }
+    Block(DebugSymRef, Vec<Statement<F, V>>),
+    /// Call into another machine with assertion and subsequent transition to another
+    /// state.
+    /// Tuple values:
+    /// - debug symbol reference;
+    /// - assigned signal IDs;
+    /// - call expression;
+    /// - next state ID;
+    HyperTransition(DebugSymRef, Vec<V>, Expression<F, V>, V),
 }
 
 impl<F: Debug> Debug for Statement<F, Identifier> {
@@ -84,6 +98,18 @@ impl<F: Debug> Debug for Statement<F, Identifier> {
                         .join(" ")
                 )
             }
+            Statement::HyperTransition(_, ids, call, state) => {
+                write!(
+                    f,
+                    "{:?} <== {:?} -> {:?};",
+                    ids.iter()
+                        .map(|id| id.name())
+                        .collect::<Vec<_>>()
+                        .join(", "),
+                    call,
+                    state
+                )
+            }
         }
     }
 }
@@ -102,6 +128,7 @@ impl<F, V> Statement<F, V> {
             Statement::StateDecl(dsym, _, _) => dsym.clone(),
             Statement::Transition(dsym, _, _) => dsym.clone(),
             Statement::Block(dsym, _) => dsym.clone(),
+            Statement::HyperTransition(dsym, _, _, _) => dsym.clone(),
         }
     }
 }
diff --git a/src/parser/build.rs b/src/parser/build.rs
index d832991d..e179f875 100644
--- a/src/parser/build.rs
+++ b/src/parser/build.rs
@@ -1,5 +1,3 @@
-use num_bigint::BigInt;
-
 use super::ast::{expression::Expression, statement::Statement, DebugSymRef, Identifier};
 
 pub fn build_bin_op<S: Into<String>, F, V>(
@@ -64,25 +62,14 @@ pub fn build_transition<F>(
     Statement::Transition(dsym, id, Box::new(block))
 }
 
-pub fn add_dsym(
+pub fn build_hyper_transition<F: Clone>(
     dsym: DebugSymRef,
-    stmt: Statement<BigInt, Identifier>,
-) -> Statement<BigInt, Identifier> {
-    match stmt {
-        Statement::Assert(_, expr) => Statement::Assert(dsym, expr),
-        Statement::SignalAssignment(_, ids, exprs) => Statement::SignalAssignment(dsym, ids, exprs),
-        Statement::SignalAssignmentAssert(_, ids, exprs) => {
-            Statement::SignalAssignmentAssert(dsym, ids, exprs)
-        }
-        Statement::WGAssignment(_, ids, exprs) => Statement::WGAssignment(dsym, ids, exprs),
-        Statement::StateDecl(_, id, block) => Statement::StateDecl(dsym, id, block),
-        Statement::IfThen(_, cond, then_block) => Statement::IfThen(dsym, cond, then_block),
-        Statement::IfThenElse(_, cond, then_block, else_block) => {
-            Statement::IfThenElse(dsym, cond, then_block, else_block)
-        }
-        Statement::Block(_, stmts) => Statement::Block(dsym, stmts),
-        Statement::SignalDecl(_, ids) => Statement::SignalDecl(dsym, ids),
-        Statement::WGVarDecl(_, ids) => Statement::WGVarDecl(dsym, ids),
-        Statement::Transition(_, id, stmt) => Statement::Transition(dsym, id, stmt),
+    ids: Vec<Identifier>,
+    call: Expression<F, Identifier>,
+    state: Identifier,
+) -> Statement<F, Identifier> {
+    match call {
+        Expression::Call(_, _, _) => Statement::HyperTransition(dsym, ids, call, state),
+        _ => unreachable!("Hyper transition must include a call statement"),
     }
 }
diff --git a/src/parser/chiquito.lalrpop b/src/parser/chiquito.lalrpop
index b8fb582c..36b50a3c 100644
--- a/src/parser/chiquito.lalrpop
+++ b/src/parser/chiquito.lalrpop
@@ -37,9 +37,9 @@ pub Statements: Vec<Statement<BigInt, Identifier>> = {
 }
 
 ParseStatement: Statement<BigInt, Identifier> = {
-    <l: @L> <s: StatementType> ";" <r: @R> => add_dsym(dsym_factory.create(l,r), s),
-    <l: @L> <s: ConditionalStatement> <r: @R> => add_dsym(dsym_factory.create(l,r), s),
-    <l: @L> <s: StateTransition> <r: @R> => add_dsym(dsym_factory.create(l,r), s),
+    <s: StatementType> ";" => s,
+    <s: ConditionalStatement> => s,
+    <s: StateTransition> => s,
 }
 
 StatementType: Statement<BigInt, Identifier> = {
@@ -53,6 +53,7 @@ StatementType: Statement<BigInt, Identifier> = {
     ParseWGVarDecl,
     ParseTransitionSimple,
     ParseTransition,
+    HyperTransition,
 }
 
 AssertEq: Statement<BigInt, Identifier> = {
@@ -111,6 +112,10 @@ ParseTransition: Statement<BigInt, Identifier> = {
     <l: @L> "->" <id: Identifier> <block: StatementsBlock> <r: @R> => build_transition(dsym_factory.create(l,r), id, block),
 }
 
+HyperTransition: Statement<BigInt, Identifier> = {
+    <l: @L> <ids: ParseIdsList> "<==" <call:Expression> "->" <st: Identifier> <r: @R> => build_hyper_transition(dsym_factory.create(l,r), ids, call, st),
+}
+
 ParseSignalDecl: Statement<BigInt, Identifier> = {
     <l: @L> "signal" <ids: ParseTypedIdList> <r: @R> => Statement::SignalDecl(dsym_factory.create(l,r), ids),
 }
@@ -196,12 +201,17 @@ ParsePrefix: Expr = {
     ExpressionTerm
 }
 
+Call: Expr = {
+    <l: @L> <fun: Identifier> "(" <es:ParseExpressionList> ")" <r: @R> => Expression::Call(dsym_factory.create(l,r), fun, es),
+}
+
 ExpressionTerm: Expr = {
     <l: @L> <id: Identifier> <r: @R> => build_query(id, dsym_factory.create(l,r)),
     <l: @L> <lit: FieldElement> <r: @R> => lit,
     <l: @L> "true" <r: @R> => Expression::True(dsym_factory.create(l,r)),
     <l: @L> "false" <r: @R> => Expression::False(dsym_factory.create(l,r)),
     <l: @L> "(" <e: Expression> ")" <r: @R> => e,
+    Call
 }
 
 ParseBinOp<Op, Next>: Expr = {