diff --git a/README.md b/README.md
index 0f07377..a828f2a 100644
--- a/README.md
+++ b/README.md
@@ -296,7 +296,7 @@ Items not marked as completed may have partial implementations.
       - [X] `be_empty`
       - [X] `have_key`
       - [X] `have_value`
-      - [ ] `all`
+      - [X] `all`
       - [ ] `all_satisfy`
     - [X] Truthy matchers - `be`, `be_true`, `be_truthy`, `be_false`, `be_falsey`, `be_nil`
     - [X] Error matchers - `raise_error`
diff --git a/src/spectator/dsl/matcher_dsl.cr b/src/spectator/dsl/matcher_dsl.cr
index 043ece4..bcfbec1 100644
--- a/src/spectator/dsl/matcher_dsl.cr
+++ b/src/spectator/dsl/matcher_dsl.cr
@@ -526,6 +526,19 @@ module Spectator::DSL
       ::Spectator::Matchers::AttributesMatcher.new(%test_value)
     end
 
+    # Verifies that all elements of a collection satisfy some matcher.
+    # The collection should implement `Enumerable`.
+    #
+    # Examples:
+    # ```
+    # array = [1, 2, 3, 4]
+    # expect(array).to all(be_even)  # Fails.
+    # expect(array).to all(be_lt(5)) # Passes.
+    # ```
+    macro all(matcher)
+      ::Spectator::Matchers::AllMatcher.new({{matcher}})
+    end
+
     # Indicates that some expression's value should change after taking an action.
     #
     # Examples:
diff --git a/src/spectator/matchers/all_matcher.cr b/src/spectator/matchers/all_matcher.cr
new file mode 100644
index 0000000..d43bda8
--- /dev/null
+++ b/src/spectator/matchers/all_matcher.cr
@@ -0,0 +1,57 @@
+require "../test_value"
+require "./failed_match_data"
+require "./matcher"
+require "./successful_match_data"
+
+module Spectator::Matchers
+  # Matcher that checks if all elements of a collection apply to some other matcher.
+  struct AllMatcher(TMatcher) < Matcher
+    # Other matcher that all elements must match successfully.
+    private getter matcher
+
+    # Creates the matcher with an expected successful matcher.
+    def initialize(@matcher : TMatcher)
+    end
+
+    # Short text about the matcher's purpose.
+    # This explains what condition satisfies the matcher.
+    # The description is used when the one-liner syntax is used.
+    def description
+      "all #{matcher.description}"
+    end
+
+    # Actually performs the test against the expression.
+    def match(actual : TestExpression(T)) : MatchData forall T
+      found = test_values(actual).each do |element|
+        match_data = matcher.match(element)
+        break match_data unless match_data.matched?
+      end
+      found ? found : SuccessfulMatchData.new
+    end
+
+    # Negated matching for this matcher is not supported.
+    # Attempting to call this method will result in a compilation error.
+    #
+    # This syntax has a logical problem.
+    # "All values do not satisfy some condition."
+    # Does this mean that all values don't satisfy the matcher?
+    # What if only one doesn't?
+    # What if the collection is empty?
+    #
+    # RSpec doesn't support this syntax either.
+    def negated_match(actual : TestExpression(T)) : MatchData forall T
+      {% raise "The `expect { }.to_not all()` syntax is not supported (ambiguous)." %}
+    end
+
+    # Maps all values in the test collection to their own test values.
+    # Each value is given their own label,
+    # which is the original label with an index appended.
+    private def test_values(actual)
+      label_prefix = actual.label
+      actual.value.map_with_index do |value, index|
+        label = "#{label_prefix}[#{index}]"
+        TestValue.new(value, label)
+      end
+    end
+  end
+end
diff --git a/src/spectator/test_block.cr b/src/spectator/test_block.cr
index b0dc53d..a6af675 100644
--- a/src/spectator/test_block.cr
+++ b/src/spectator/test_block.cr
@@ -16,7 +16,7 @@ module Spectator
 
     def self.create(proc : -> T, label : String) forall T
       {% if T.id == "ReturnType".id %}
-        wrapper = -> { proc.call; nil }
+        wrapper = ->{ proc.call; nil }
         TestBlock(Nil).new(wrapper, label)
       {% else %}
         TestBlock(T).new(proc, label)
@@ -31,7 +31,7 @@ module Spectator
 
     def self.create(proc : -> T) forall T
       {% if T.id == "ReturnType".id %}
-        wrapper = -> { proc.call; nil }
+        wrapper = ->{ proc.call; nil }
         TestBlock(Nil).new(wrapper)
       {% else %}
         TestBlock(T).new(proc)