diff --git a/Hype.rb b/Hype.rb
index a1695a8..f354c09 100644
--- a/Hype.rb
+++ b/Hype.rb
@@ -20,6 +20,7 @@ module Hype
     rb    - generate Ruby files to HyperTensioN
     cpp   - generate C++ file with HyperTensioN
     pddl  - generate PDDL files
+    hddl  - generate HDDL files
     jshop - generate JSHOP files
     dot   - generate DOT file
     md    - generate Markdown file
@@ -169,6 +170,7 @@ def compile(domain, problem, type)
     when 'rb' then Hyper_Compiler
     when 'cpp' then Cyber_Compiler
     when 'jshop' then JSHOP_Compiler
+    when 'hddl' then HDDL_Compiler
     when 'pddl' then PDDL_Compiler
     when 'dot' then Dot_Compiler
     when 'md' then Markdown_Compiler
diff --git a/README.md b/README.md
index f4dacf7..dff29ea 100644
--- a/README.md
+++ b/README.md
@@ -132,6 +132,7 @@ Output:
   rb    - generate Ruby files to HyperTensioN
   cpp   - generate C++ file with HyperTensioN
   pddl  - generate PDDL files
+  hddl  - generate HDDL files
   jshop - generate JSHOP files
   dot   - generate DOT file
   md    - generate Markdown file
@@ -195,6 +196,7 @@ Hype is composed of:
 - Hyper (methods and tasks are unavailable for a PDDL input without extensions)
 - Cyber (methods and tasks are unavailable for a PDDL input without extensions)
 - [PDDL] (methods are ignored, goal must be manually converted based on tasks)
+- [HDDL] (methods and tasks are unavailable for a PDDL input without extensions)
 - [JSHOP] (methods and tasks are unavailable for a PDDL input without extensions)
 - [Graphviz DOT](https://www.graphviz.org/) (generate a [graph](docs/Graph.md) description to be compiled into an image)
 - [Markdown](https://daringfireball.net/projects/markdown/)
@@ -390,6 +392,8 @@ Unordered tasks are supported only at the problem level and are not interleaved
   - Skip invisible operators as subtasks in Macro
 - Oct 2023
   - Support unordered tasks in Macro
+- Mar 2024
+  - Add HDDL compiler
 
 </details>
 
diff --git a/compilers/HDDL_Compiler.rb b/compilers/HDDL_Compiler.rb
new file mode 100644
index 0000000..0e5fd6d
--- /dev/null
+++ b/compilers/HDDL_Compiler.rb
@@ -0,0 +1,94 @@
+module HDDL_Compiler
+  extend self
+
+  #-----------------------------------------------
+  # Compile domain
+  #-----------------------------------------------
+
+  def compile_domain(domain_name, problem_name, operators, methods, predicates, state, tasks, goal_pos, goal_not)
+    negative_preconditions = method_preconditions = false
+    declared = {}
+    action_str = ''
+    # Operators
+    operators.each {|op|
+      # Header
+      action_str << "\n  (:action #{op[0]}\n    :parameters (#{op[1].join(' ')})\n    :precondition (and\n"
+      # Preconditions
+      op[2].each {|pre| action_str << "      (#{pre.join(' ')})\n"; declared[pre[0]] ||= pre}
+      op[3].each {|pre| action_str << "      (not (#{pre.join(' ')}))\n"; declared[pre[0]] ||= pre}
+      negative_preconditions = true unless op[3].empty?
+      # Effects
+      action_str << "    )\n    :effect (and\n"
+      op[4].each {|pre| action_str << "      (#{pre.join(' ')})\n"; declared[pre[0]] ||= pre}
+      op[5].each {|pre| action_str << "      (not (#{pre.join(' ')}))\n"; declared[pre[0]] ||= pre}
+      action_str << "    )\n  )\n"
+    }
+    # Methods
+    methods.each {|met|
+      action_str << "\n  (:task #{met[0]} :parameters (#{met[1].join(' ')}))"
+      task = "\n    :task (#{met[0]} #{met[1].join(' ')})\n    "
+      met.drop(2).each {|dec|
+        # Header
+        action_str << "\n  (:method #{dec[0]}\n    :parameters (#{(met[1] + dec[1]).join(' ')})#{task}:precondition (and\n"
+        # Preconditions
+        dec[2].each {|pre| action_str << "      (#{pre.join(' ')})\n"; declared[pre[0]] ||= pre}
+        dec[3].each {|pre| action_str << "      (not (#{pre.join(' ')}))\n"; declared[pre[0]] ||= pre}
+        method_preconditions = true unless dec[2].empty?
+        method_preconditions = negative_preconditions = true unless dec[3].empty?
+        # Subtasks
+        action_str << "    )\n    :ordered-subtasks (and\n"
+        dec[4].each {|task| action_str << "      (#{task.join(' ')})\n"}
+        action_str << "    )\n  )\n"
+      }
+    }
+    goal_pos.each {|pre| declared[pre[0]] ||= pre}
+    goal_not.each {|pre| declared[pre[0]] ||= pre}
+    domain_str = "; Generated by Hype\n(define (domain #{domain_name})
+#  (:requirements :hierarchy#{' :negative-preconditions' if negative_preconditions}#{' :method-preconditions' if method_preconditions}#{' :equality' if declared.delete('=')})\n\n  (:predicates\n"
+    declared.each_value {|pre|
+      (pre = pre.join(' ?')).squeeze!('?')
+      domain_str << "    (#{pre})\n"
+    }
+    domain_str << "  )\n" << action_str << ')'
+  end
+
+  #-----------------------------------------------
+  # Compile problem
+  #-----------------------------------------------
+
+  def compile_problem(domain_name, problem_name, operators, methods, predicates, state, tasks, goal_pos, goal_not, domain_filename)
+    objects = []
+    start_str = ''
+    state.each {|pre,k|
+      objects.concat(k.each {|terms|
+        start_str << "    (#{terms.unshift(pre).join(' ')})\n"
+        terms.shift
+      }.flatten(1)) if pre != '=' and predicates.include?(pre)
+    }
+    tasks_str = ''
+    tasks.drop(1).each {|pre|
+      objects.concat(pre.drop(1))
+      tasks_str << "    (#{pre.join(' ')})\n"
+    }
+    unless goal_pos.empty? and goal_not.empty?
+      goal_str = "(:goal (and\n"
+      goal_pos.each {|pre|
+        objects.concat(pre.drop(1))
+        goal_str << "    (#{pre.join(' ')})\n"
+      }
+      goal_not.each {|pre|
+        objects.concat(pre.drop(1))
+        goal_str << "    (not (#{pre.join(' ')}))\n"
+      }
+      goal_str << "  ))\n  "
+    end
+    objects.uniq!
+"; Generated by Hype
+(define (problem #{problem_name})
+  (:domain #{domain_name})
+  (:objects\n    #{objects.join(' ')}\n  )
+  (:init\n#{start_str}  )
+  #{goal_str}(:htn :ordered-tasks (and
+#{tasks_str}  ))\n)"
+  end
+end
\ No newline at end of file