diff --git a/lib/networkx/graph.rb b/lib/networkx/graph.rb
index 84d5be9..25a632c 100644
--- a/lib/networkx/graph.rb
+++ b/lib/networkx/graph.rb
@@ -1,40 +1,44 @@
 module NetworkX
   class Graph
     def initialize
-      @nodes = Set.new
-      @edges = {}
+      @adj = {}
+    end
+
+    def add_node(node)
+      @adj[node] = {} unless @adj.key? node
+    end
+
+    def add_nodes_from(nodes)
+      nodes.each { |node| add_node(node) }
     end
 
     def add_edge(node_1, node_2, **attrs)
       add_node(node_1)
       add_node(node_2)
 
-      edge_key         = Set.new([node_1, node_2])
-      @edges[edge_key] = attrs
+      @adj[node_1][node_2] = attrs
     end
 
-    def add_edges(edges)
-      case edges
-      when Array
-        edges.each { |node_1, node_2, **attrs| add_edge(node_1, node_2, **attrs) }
-      else
-        raise ArgumentError, 'Expected argument to be an Array of edges, '\
-                             "received #{edges.class.name} instead."
-      end
+    def add_edges_from(edges)
+      edges.each { |edge| add_edge(*edge) }
     end
 
-    def add_node(node)
-      @nodes.add(node)
+    def remove_node(node)
+      @adj.delete(node)
+      @adj.each_key { |key| @adj[key].delete(node) }
+    end
+
+    def remove_nodes_from(nodes)
+      nodes.each { |node| @adj.delete(node) }
+      nodes.each { |node| @adj.each_key { |key| @adj[key].delete(node) } }
+    end
+
+    def remove_edge(node_1, node_2)
+      @adj[node_1].delete(node_2) if @adj.key? node_1
     end
 
-    def add_nodes(nodes)
-      case nodes
-      when Set, Array
-        nodes.each { |node| add_node(node) }
-      else
-        raise ArgumentError, 'Expected argument to be an Array or Set of nodes, '\
-                             "received #{nodes.class.name} instead."
-      end
+    def remove_edges_from(edges)
+      edges.each { |edge| remove_edge(*edge) }
     end
   end
 end