diff --git a/src/spectator/expectations/block_expectation.cr b/src/spectator/expectations/block_expectation.cr
new file mode 100644
index 0000000..ba30de6
--- /dev/null
+++ b/src/spectator/expectations/block_expectation.cr
@@ -0,0 +1,31 @@
+require "./expectation"
+
+module Spectator::Expectations
+  # Expectation that operates on a block.
+  # A block produces some value one or more times.
+  # A matcher checks whether the values produced by the block satisfy some conditions.
+  # The behavior of the block can be tested by verifying the values produced by it.
+  class BlockExpectation(ReturnType) < Expectation
+    # Creates the expectation.
+    # The `matched` flag should be true if the matcher is satisfied with the partial.
+    # The `negated` flag should be true if the expectation is inverted.
+    # See `Expectation#initialize` for details on these two arguments.
+    # The `partial` and the `matcher` arguments should reference
+    # the actual and expected value with matcher respectively.
+    def initialize(matched, negated,
+                   @partial : BlockExpectationPartial(ReturnType),
+                   @matcher : Matchers::Matcher)
+      super(matched, negated)
+    end
+
+    # Describes the condition that must be met for the expectation to be satisifed.
+    private def message : String
+      @matcher.message(@partial)
+    end
+
+    # Describes the condition under which the expectation won't be satisifed.
+    private def negated_message : String
+      @matcher.negated_message(@partial)
+    end
+  end
+end
diff --git a/src/spectator/expectations/block_expectation_partial.cr b/src/spectator/expectations/block_expectation_partial.cr
new file mode 100644
index 0000000..12efac5
--- /dev/null
+++ b/src/spectator/expectations/block_expectation_partial.cr
@@ -0,0 +1,31 @@
+require "./expectation_partial"
+
+module Spectator::Expectations
+  # Expectation partial variation that operates on a block.
+  struct BlockExpectationPartial(ReturnType) < ExpectationPartial
+    # Actual value produced by calling the block.
+    def actual
+      @block.call
+    end
+
+    # Creates the expectation partial.
+    # The label should be a string representation of the block.
+    # The block is stored for later use.
+    protected def initialize(label : String, @block : -> ReturnType)
+      super(label)
+    end
+
+    # Creates the expectation partial.
+    # The label is generated by calling `#to_s` on the block.
+    # The block is stored for later use.
+    protected def initialize(@block : -> ReturnType)
+      super(@block.to_s)
+    end
+
+    # Evaluates the expectation and returns it.
+    private def eval(matcher, negated = false) : Expectation
+      matched = matcher.match?(self)
+      BlockExpectation.new(matched, negated, self, matcher)
+    end
+  end
+end