diff --git a/builtin/core.wren b/builtin/core.wren
index a3722dd9..a127cdda 100644
--- a/builtin/core.wren
+++ b/builtin/core.wren
@@ -26,21 +26,9 @@ class Sequence {
     return result
   }
 
-  map(f) {
-    var result = new List
-    for (element in this) {
-      result.add(f.call(element))
-    }
-    return result
-  }
+  map(transformation) { new MapSequence(this, transformation) }
 
-  where(f) {
-    var result = new List
-    for (element in this) {
-      if (f.call(element)) result.add(element)
-    }
-    return result
-  }
+  where(predicate) { new WhereSequence(this, predicate) }
 
   all(f) {
     for (element in this) {
@@ -100,6 +88,32 @@ class Sequence {
   }
 }
 
+class MapSequence is Sequence {
+  new(seq, f) {
+    _seq = seq
+    _f = f
+  }
+
+  iterate(n) { _seq.iterate(n) }
+  iteratorValue(iterator) { _f.call(_seq.iteratorValue(iterator)) }
+}
+
+class WhereSequence is Sequence {
+  new(seq, f) {
+    _seq = seq
+    _f = f
+  }
+
+  iterate(n) {
+    while (n = _seq.iterate(n)) {
+      if (_f.call(_seq.iteratorValue(n))) break
+    }
+    return n
+  }
+
+  iteratorValue(iterator) { _seq.iteratorValue(iterator) }
+}
+
 class String is Sequence {
   bytes { new StringByteSequence(this) }
 }
diff --git a/doc/site/core/sequence.markdown b/doc/site/core/sequence.markdown
index 807e6c84..c8a6c8d4 100644
--- a/doc/site/core/sequence.markdown
+++ b/doc/site/core/sequence.markdown
@@ -74,14 +74,13 @@ Creates a [list](list.html) containing all the elements in the sequence.
 
 ### **map**(transformation)
 
-Creates a new list by applying `transformation` to each element in the
-sequence.
+Creates a new sequence that applies the `transformation` to each element in the
+original sequence while it is iterated.
 
-Iterates over the sequence, passing each element to the function
-`transformation`. Generates a new list from the result of each of those calls.
+The `list` method can be used to turn the resulting sequence into a list.
 
     :::dart
-    [1, 2, 3].map {|n| n * 2} // [2, 4, 6].
+    [1, 2, 3].map {|n| n * 2}.list // [2, 4, 6].
 
 ### **reduce**(function)
 
@@ -95,10 +94,13 @@ Similar to above, but uses `seed` for the initial value of the accumulator. If t
 
 ### **where**(predicate)
 
-Produces a new list containing only the elements in the sequence that pass the
-`predicate`.
+Creates a new sequence containing only the elements from the original sequence
+that pass the `predicate`.
 
-Iterates over the sequence, passing each element to the function `predicate`.
-If it returns `true`, adds the element to the result list.
+During iteration, each element in the original sequence is passed to the
+function `predicate`. If it returns `false`, the element is skipped.
 
-    (1..10).where {|n| n % 2 == 1} // [1, 3, 5, 7, 9].
+The `list` method can be used to turn the resulting sequence into a list.
+
+    :::dart
+    (1..10).where {|n| n % 2 == 1}.list // [1, 3, 5, 7, 9].
diff --git a/src/vm/wren_core.c b/src/vm/wren_core.c
index ea75e896..93440552 100644
--- a/src/vm/wren_core.c
+++ b/src/vm/wren_core.c
@@ -72,21 +72,9 @@ static const char* libSource =
 "    return result\n"
 "  }\n"
 "\n"
-"  map(f) {\n"
-"    var result = new List\n"
-"    for (element in this) {\n"
-"      result.add(f.call(element))\n"
-"    }\n"
-"    return result\n"
-"  }\n"
+"  map(transformation) { new MapSequence(this, transformation) }\n"
 "\n"
-"  where(f) {\n"
-"    var result = new List\n"
-"    for (element in this) {\n"
-"      if (f.call(element)) result.add(element)\n"
-"    }\n"
-"    return result\n"
-"  }\n"
+"  where(predicate) { new WhereSequence(this, predicate) }\n"
 "\n"
 "  all(f) {\n"
 "    for (element in this) {\n"
@@ -146,6 +134,32 @@ static const char* libSource =
 "  }\n"
 "}\n"
 "\n"
+"class MapSequence is Sequence {\n"
+"  new(seq, f) {\n"
+"    _seq = seq\n"
+"    _f = f\n"
+"  }\n"
+"\n"
+"  iterate(n) { _seq.iterate(n) }\n"
+"  iteratorValue(iterator) { _f.call(_seq.iteratorValue(iterator)) }\n"
+"}\n"
+"\n"
+"class WhereSequence is Sequence {\n"
+"  new(seq, f) {\n"
+"    _seq = seq\n"
+"    _f = f\n"
+"  }\n"
+"\n"
+"  iterate(n) {\n"
+"    while (n = _seq.iterate(n)) {\n"
+"      if (_f.call(_seq.iteratorValue(n))) break\n"
+"    }\n"
+"    return n\n"
+"  }\n"
+"\n"
+"  iteratorValue(iterator) { _seq.iteratorValue(iterator) }\n"
+"}\n"
+"\n"
 "class String is Sequence {\n"
 "  bytes { new StringByteSequence(this) }\n"
 "}\n"
diff --git a/test/core/list/map.wren b/test/core/list/map.wren
index 4ed3778a..5eb759a1 100644
--- a/test/core/list/map.wren
+++ b/test/core/list/map.wren
@@ -1,3 +1,3 @@
 var a = [1, 2, 3]
-var b = a.map {|x| x + 1 }
+var b = a.map {|x| x + 1 }.list
 IO.print(b) // expect: [2, 3, 4]
diff --git a/test/core/list/where.wren b/test/core/list/where.wren
index ebc4a228..ab451bde 100644
--- a/test/core/list/where.wren
+++ b/test/core/list/where.wren
@@ -1,6 +1,6 @@
 var a = [1, 2, 3]
-var b = a.where {|x| x > 1 }
+var b = a.where {|x| x > 1 }.list
 IO.print(b) // expect: [2, 3]
 
-var c = a.where {|x| x > 10 }
+var c = a.where {|x| x > 10 }.list
 IO.print(c) // expect: []
diff --git a/test/core/range/map.wren b/test/core/range/map.wren
index 73766961..85d6fc25 100644
--- a/test/core/range/map.wren
+++ b/test/core/range/map.wren
@@ -1,3 +1,3 @@
 var a = 1..3
-var b = a.map {|x| x + 1 }
+var b = a.map {|x| x + 1 }.list
 IO.print(b) // expect: [2, 3, 4]
diff --git a/test/core/range/where.wren b/test/core/range/where.wren
index 796b4585..0a90e17a 100644
--- a/test/core/range/where.wren
+++ b/test/core/range/where.wren
@@ -1,6 +1,6 @@
 var a = 1..3
-var b = a.where {|x| x > 1 }
+var b = a.where {|x| x > 1 }.list
 IO.print(b) // expect: [2, 3]
 
-var c = a.where {|x| x > 10 }
+var c = a.where {|x| x > 10 }.list
 IO.print(c) // expect: []
diff --git a/test/core/sequence/map.wren b/test/core/sequence/map.wren
new file mode 100644
index 00000000..45beba20
--- /dev/null
+++ b/test/core/sequence/map.wren
@@ -0,0 +1,46 @@
+// Infinite iterator demonstrating that Sequence.map is not eager
+class FibIterator {
+  new {
+    _current = 0
+    _next = 1
+  }
+
+  iterate {
+    var sum = _current + _next
+    _current = _next
+    _next = sum
+  }
+
+  value { _current }
+}
+
+class Fib is Sequence {
+  iterate(iterator) {
+    if (iterator == null) return new FibIterator
+    iterator.iterate
+    return iterator
+  }
+
+  iteratorValue(iterator) { iterator.value }
+}
+
+var squareFib = (new Fib).map {|fib| fib * fib }
+var iterator = null
+
+IO.print(squareFib is Sequence) // expect: true
+IO.print(squareFib) // expect: instance of MapSequence
+
+iterator = squareFib.iterate(iterator)
+IO.print(squareFib.iteratorValue(iterator)) // expect: 0
+
+iterator = squareFib.iterate(iterator)
+IO.print(squareFib.iteratorValue(iterator)) // expect: 1
+
+iterator = squareFib.iterate(iterator)
+IO.print(squareFib.iteratorValue(iterator)) // expect: 1
+
+iterator = squareFib.iterate(iterator)
+IO.print(squareFib.iteratorValue(iterator)) // expect: 4
+
+iterator = squareFib.iterate(iterator)
+IO.print(squareFib.iteratorValue(iterator)) // expect: 9
diff --git a/test/core/sequence/where.wren b/test/core/sequence/where.wren
new file mode 100644
index 00000000..e641ab22
--- /dev/null
+++ b/test/core/sequence/where.wren
@@ -0,0 +1,40 @@
+// Infinite iterator demonstrating that Sequence.where is not eager
+class FibIterator {
+  new {
+    _current = 0
+    _next = 1
+  }
+
+  iterate {
+    var sum = _current + _next
+    _current = _next
+    _next = sum
+  }
+
+  value { _current }
+}
+
+class Fib is Sequence {
+  iterate(iterator) {
+    if (iterator == null) return new FibIterator
+    iterator.iterate
+    return iterator
+  }
+
+  iteratorValue(iterator) { iterator.value }
+}
+
+var largeFibs = (new Fib).where {|fib| fib > 100 }
+var iterator = null
+
+IO.print(largeFibs is Sequence) // expect: true
+IO.print(largeFibs) // expect: instance of WhereSequence
+
+iterator = largeFibs.iterate(iterator)
+IO.print(largeFibs.iteratorValue(iterator)) // expect: 144
+
+iterator = largeFibs.iterate(iterator)
+IO.print(largeFibs.iteratorValue(iterator)) // expect: 233
+
+iterator = largeFibs.iterate(iterator)
+IO.print(largeFibs.iteratorValue(iterator)) // expect: 377