diff --git a/lib/src/io/github/alechenninger/monarch/Assignments.java b/lib/src/io/github/alechenninger/monarch/Assignments.java
index 082ed3b..d06c923 100644
--- a/lib/src/io/github/alechenninger/monarch/Assignments.java
+++ b/lib/src/io/github/alechenninger/monarch/Assignments.java
@@ -20,6 +20,7 @@
 
 import java.util.Collection;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.Iterator;
 import java.util.LinkedHashSet;
 import java.util.List;
@@ -34,6 +35,7 @@
 public class Assignments implements Iterable<Assignment> {
   private final Set<Assignment> explicit = new LinkedHashSet<>();
   private final Set<Assignment> implicit = new LinkedHashSet<>();
+  private final Map<String, Assignment> byVariable = new HashMap<>();
   private final Inventory inventory;
 
   private final int hash;
@@ -119,12 +121,11 @@ public Assignments forkAt(String variable) {
   }
 
   public boolean isAssigned(String variable) {
-    return stream().anyMatch(a -> a.variable().name().equals(variable));
+    return byVariable.containsKey(variable);
   }
 
   public Assignment forVariable(String variable) {
-    return stream().filter(a -> a.variable().name().equals(variable))
-        .findAny()
+    return Optional.ofNullable(byVariable.get(variable))
         .orElseThrow(NoSuchElementException::new);
   }
 
@@ -255,7 +256,7 @@ public Map<String, String> toMap() {
   }
 
   public Stream<Assignment> stream() {
-    return Stream.concat(explicit.stream(), implicit.stream());
+    return byVariable.values().stream();
   }
 
   @Override
@@ -332,6 +333,7 @@ private void add(Assignment assignment) {
     }
 
     explicit.add(assignment);
+    byVariable.put(variable.name(), assignment);
     assignment.implied().forEach(this::addImplicit);
   }
 
@@ -347,6 +349,7 @@ private void addImplicit(Assignment assignment) {
     }
 
     this.implicit.add(assignment);
+    byVariable.put(assignment.variable().name(), assignment);
     assignment.implied().forEach(this::addImplicit);
   }
 
diff --git a/lib/src/io/github/alechenninger/monarch/Variable.java b/lib/src/io/github/alechenninger/monarch/Variable.java
index 8fb2a4b..629a7e1 100644
--- a/lib/src/io/github/alechenninger/monarch/Variable.java
+++ b/lib/src/io/github/alechenninger/monarch/Variable.java
@@ -19,6 +19,7 @@
 package io.github.alechenninger.monarch;
 
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
@@ -32,6 +33,8 @@ public class Variable {
   private final List<Assignable> assignables;
   private final Inventory inventory;
 
+  private final Map<String, Assignment> cachedAssignments = new HashMap<>();
+
   public Variable(String name, List<Assignable> assignables, Inventory inventory) {
     this.name = Objects.requireNonNull(name, "name");
     this.assignables = Objects.requireNonNull(assignables, "assignables");
@@ -76,18 +79,27 @@ public Set<String> values(Assignments assignments) {
   }
 
   public Assignment assign(String value) {
-    Optional<Assignable> assignable = assignables.stream()
-        .filter(a -> a.value().equals(value))
-        .findFirst();
+    Assignment assignment;
+
+    if (cachedAssignments.containsKey(value)) {
+      assignment = cachedAssignments.get(value);
+    } else {
+      assignment = assignables.stream()
+          .filter(a -> a.value().equals(value))
+          .findFirst()
+          .map(a -> new Assignment(inventory, this, a))
+          .orElse(null);
+      cachedAssignments.put(value, assignment);
+    }
 
-    if (!assignable.isPresent()) {
+    if (assignment == null) {
       throw new IllegalArgumentException("Cannot assign value <" + value + "> to variable <" +
           name + "> because value is not assignable for this variable. Check your assignment or " +
           "add value to inventory. An inventory needs to be comprehensive so it can be used to " +
           "discover all of the sources in your hierarchy.");
     }
 
-    return new Assignment(inventory, this, assignable.get());
+    return assignment;
   }
 
   @Override