diff --git a/ChangeLog b/ChangeLog
index 16ce2e8bac..d4427fca79 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sat Dec 27 09:14:17 2008  Yuki Sonoda (Yugui)  <yugui@yugui.jp>
+
+	* cont.c: rdoc for Fiber. patch by Muhammad Ali.
+	  [ruby-core:20894]
+
 Sat Dec 27 05:38:59 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* process.c (after_fork): ignores a termination request in the
diff --git a/cont.c b/cont.c
index 10912e4c35..22c7fb3720 100644
--- a/cont.c
+++ b/cont.c
@@ -570,6 +570,68 @@ rb_cont_call(int argc, VALUE *argv, VALUE contval)
 /* fiber */
 /*********/
 
+/*
+ *  Document-class: Fiber
+ *
+ *  Fibers are primitives for implementing light weight cooperative
+ *  concurrency in Ruby. Basically they are a means of creating code blocks 
+ *  that can be paused and resumed, much like threads. The main difference 
+ *  is that they are never preempted and that the scheduling must be done by 
+ *  the programmer and not the VM. 
+ *
+ *  As opposed to other stackless light weight concurrency models, each fiber
+ *  comes with a small 4KB stack. This enables the fiber to be paused from deeply
+ *  nested function calls within the fiber block.
+ *
+ *  When a fiber is created it will not run automatically. Rather it must be 
+ *  be explicitly asked to run using the <code>Fiber#resume</code> method. 
+ *  The code running inside the fiber can give up control by calling 
+ *  <code>Fiber.yield</code> in which case it yields control back to caller 
+ *  (the caller of the <code>Fiber#resume</code>).
+ * 
+ *  Upon yielding or termination the Fiber returns the value of the last 
+ *  executed expression
+ *  
+ *  For instance:
+ *  
+ *    fiber = Fiber.new do
+ *      Fiber.yield 1
+ *      2
+ *    end
+ *
+ *    puts fiber.resume
+ *    puts fiber.resume
+ *    puts fiber.resume
+ *    
+ *  <em>produces</em>
+ *    
+ *    1
+ *    2
+ *    FiberError: dead fiber called
+ *     
+ *  The <code>Fiber#resume</code> method accepts an arbitary number of
+ *  parameters, if it is the first call to <code>resume</code> then they
+ *  will be passed as block arguments. Other wise they will be the return
+ *  value of the call to <code>Fiber.yield</code>
+ *
+ *  Example:
+ *  
+ *    fiber = Fiber.new do |first|
+ *      second = Fiber.yield first + 2
+ *    end
+ *
+ *    puts fiber.resume 10
+ *    puts fiber.resume 14
+ *    puts fiber.resume 18
+ *
+ *  <em>produces</em>
+ *    
+ *    12
+ *    14
+ *    FiberError: dead fiber called
+ *
+ */
+
 #define FIBER_VM_STACK_SIZE (4 * 1024)
 
 static VALUE
@@ -840,6 +902,14 @@ rb_fiber_yield(int argc, VALUE *argv)
     return rb_fiber_transfer(return_fiber(), argc, argv);
 }
 
+/*
+ *  call-seq:
+ *     fiber.alive? -> true or false
+ *  
+ *  Returns true if the fiber can still be resumed (or transferred to).
+ *  After finishing execution of the fiber block this method will always
+ *  return false.
+ */
 VALUE
 rb_fiber_alive_p(VALUE fibval)
 {
@@ -848,24 +918,73 @@ rb_fiber_alive_p(VALUE fibval)
     return fib->status != TERMINATED;
 }
 
+/*
+ *  call-seq:
+ *     fiber.resume(args, ...) -> obj
+ *  
+ *  Resumes the fiber from the point at which the last <code>Fiber.yield</code>
+ *  was called, or starts running it if it is the first call to 
+ *  <code>resume</code>. Arguments passed to resume will be the value of
+ *  the <code>Fiber.yield</code> expression or will be passed as block 
+ *  parameters to the fiber's block if this is the first <code>resume</code>.
+ *  
+ *  Alternatively, when resume is called it evaluates to the arguments passed
+ *  to the next <code>Fiber.yield</code> statement inside the fiber's block
+ *  or to the block value if it runs to completion without any
+ *  <code>Fiber.yield</code>
+ */
 static VALUE
 rb_fiber_m_resume(int argc, VALUE *argv, VALUE fib)
 {
     return rb_fiber_resume(fib, argc, argv);
 }
 
+/*
+ *  call-seq:
+ *     fiber.transfer(args, ...) -> obj
+ *  
+ *  Transfer control to another fiber, resuming it from where it last
+ *  stopped or starting it if it was not resumed before. The calling 
+ *  fiber will be suspended much like in a call to <code>Fiber.yield</code>.
+ *  
+ *  The fiber which recieves the transfer call is treats it much like 
+ *  a resume call. Arguments passed to transfer are treated like those
+ *  passed to resume.
+ *     
+ *  You cannot resume a fiber that transferred control to another one.
+ *  This will cause a double resume error. You need to transfer control
+ *  back to this fiber before it can yield and resume.
+ */
 static VALUE
 rb_fiber_m_transfer(int argc, VALUE *argv, VALUE fib)
 {
     return rb_fiber_transfer(fib, argc, argv);
 }
 
+/*
+ *  call-seq:
+ *     Fiber.yield(args, ...) -> obj
+ *  
+ *  Yields control back to the context that resumed the fiber, passing
+ *  along any arguments that were passed to it. The fiber will resume
+ *  processing at this point when <code>resume</code> is called next.
+ *  Any arguments passed to the next <code>resume</code> will be the
+ *  value that this <code>Fiber.yield</code> expression evaluates to.
+ */
 static VALUE
 rb_fiber_s_yield(int argc, VALUE *argv, VALUE klass)
 {
     return rb_fiber_yield(argc, argv);
 }
 
+/*
+ *  call-seq:
+ *     Fiber.current() -> fiber
+ *  
+ *  Returns the current fiber. You need to <code>require 'fiber'</code>
+ *  before using this method. If you are not running in the context of
+ *  a fiber this method will return the root fiber.
+ */
 static VALUE
 rb_fiber_s_current(VALUE klass)
 {