diff --git a/README.md b/README.md
index 97f106c..1ed6887 100644
--- a/README.md
+++ b/README.md
@@ -425,6 +425,14 @@ calculator.evaluate("replace(diff(f(2*t, t+1), t), t, 3)")
 #=> 1+8*3
 ```
 
+There is also a `puts` function that can be used to output the result of an expression to STDOUT.
+
+```ruby
+calculator = Keisan::Calculator.new
+calculator.evaluate("x = 5")
+calculator.evaluate("puts x**2") # prints "25\n" to STDOUT
+```
+
 ### Adding custom variables and functions
 
 The `Keisan::Calculator` class has a single `Keisan::Context` object in its `context` attribute.  This class is used to store local variables and functions.  These can be stored using either the `define_variable!` or `define_function!` methods, or by using the assignment operator `=` in an expression that is evaluated.  As an example of pre-defining some variables and functions, see the following
diff --git a/lib/keisan/functions/default_registry.rb b/lib/keisan/functions/default_registry.rb
index 8707c11..d8d3af6 100644
--- a/lib/keisan/functions/default_registry.rb
+++ b/lib/keisan/functions/default_registry.rb
@@ -1,4 +1,5 @@
 require_relative "let"
+require_relative "puts"
 
 require_relative "if"
 require_relative "while"
@@ -46,6 +47,7 @@ def self.registry
 
       def self.register_defaults!(registry)
         registry.register!(:let, Let.new, force: true)
+        registry.register!(:puts, Puts.new, force: true)
 
         registry.register!(:if, If.new, force: true)
         registry.register!(:while, While.new, force: true)
diff --git a/lib/keisan/functions/puts.rb b/lib/keisan/functions/puts.rb
new file mode 100644
index 0000000..3e3b525
--- /dev/null
+++ b/lib/keisan/functions/puts.rb
@@ -0,0 +1,23 @@
+module Keisan
+  module Functions
+    class Puts < Function
+      def initialize
+        super("puts", 1)
+      end
+
+      def value(ast_function, context = nil)
+        evaluate(ast_function, context)
+      end
+
+      def evaluate(ast_function, context = nil)
+        validate_arguments!(ast_function.children.count)
+        puts ast_function.children.first.evaluate(context).to_s
+        Keisan::AST::Null.new
+      end
+
+      def simplify(ast_function, context = nil)
+        evaluate(ast_function, context)
+      end
+    end
+  end
+end
diff --git a/lib/keisan/parser.rb b/lib/keisan/parser.rb
index e46d0b0..e18e78b 100644
--- a/lib/keisan/parser.rb
+++ b/lib/keisan/parser.rb
@@ -1,6 +1,6 @@
 module Keisan
   class Parser
-    KEYWORDS = %w(let).freeze
+    KEYWORDS = %w(let puts).freeze
 
     attr_reader :tokens, :components
 
diff --git a/spec/keisan/puts_spec.rb b/spec/keisan/puts_spec.rb
new file mode 100644
index 0000000..c95a2b7
--- /dev/null
+++ b/spec/keisan/puts_spec.rb
@@ -0,0 +1,40 @@
+require "spec_helper"
+
+RSpec.describe Keisan::Functions::Puts do
+  let(:calculator) { Keisan::Calculator.new }
+
+  it "outputs to STDOUT" do
+    expect { calculator.evaluate("puts 123") }.to output("123\n").to_stdout
+    expect { calculator.evaluate("puts(x**2 + 1)") }.to output("(x**2)+1\n").to_stdout
+    calculator.evaluate("x = 2")
+    expect { calculator.evaluate("puts(x**2 + 1)") }.to output("5\n").to_stdout
+  end
+
+  describe "evaluate" do
+    it "returns null" do
+      expect {
+        ast = calculator.ast("puts x = 5")
+        expect(ast.evaluate).to eq Keisan::AST::Null.new
+      }.to output("5\n").to_stdout
+    end
+
+    it "does evaluation of arguments" do
+      expect { calculator.evaluate("puts(x = 12)") }.to output("12\n").to_stdout
+      expect(calculator.evaluate("x")).to eq 12
+    end
+  end
+
+  describe "#value and #simplify call evaluate" do
+    it "value calls evaluate" do
+      expect_any_instance_of(Keisan::Functions::Puts).to receive(:evaluate).and_return(Keisan::AST::Null.new)
+      ast = calculator.ast("puts x = 5")
+      expect(ast.value).to eq Keisan::AST::Null.new
+    end
+
+    it "simplify calls evaluate" do
+      expect_any_instance_of(Keisan::Functions::Puts).to receive(:evaluate).and_return(Keisan::AST::Null.new)
+      ast = calculator.ast("puts x = 5")
+      expect(ast.simplify).to eq Keisan::AST::Null.new
+    end
+  end
+end
diff --git a/spec/readme_spec.rb b/spec/readme_spec.rb
index 52da946..2c758f6 100644
--- a/spec/readme_spec.rb
+++ b/spec/readme_spec.rb
@@ -13,7 +13,7 @@
       digest = Digest::SHA256.hexdigest(content)
 
       # cat README.md | sha256sum
-      expected_digest = "ceca07925099af54db28079b7ae408bbf1d478ebe96c26c0deb1c1b0a458e194"
+      expected_digest = "ec824b6fb3574ec4c5ffab47e4c39c86573fad0f3fd7c73a8c24e55c32fee9fc"
       if digest != expected_digest
         raise "Invalid README file detected with SHA256 digest of #{digest}. Use command `cat README.md | sha256sum` to get correct digest if your changes to the README are safe. Aborting README test."
       end
@@ -25,7 +25,11 @@
 
         outputs = code_block.map do |line|
           begin
-            eval(line, b)
+            # Capture output of any `puts` statements
+            $stdout = StringIO.new
+            result = eval(line, b)
+            $stdout = STDOUT
+            result
           rescue Keisan::Exceptions::BaseError => e
             e
           end