Just to expand a little on the "you can take any loop and transform it into a tail recursion" (because I think it's cool), here's an example:

Python iterative solution

  1.  def fib(n):
  2.      i, curr, next = 0, 0, 1
  3.      while i < n:
  4.          i += 1
  5.          curr, next = next, curr + next
  6.      return curr

Python tail-recursive solution*

  1.  def fib(n):
  2.      def fib_tail(i, curr, next):                  #1
  3.          if i >= n:                                #2
  4.              return curr                           #3
  5.          return fib_tail(i+1, next, curr+next)     #4
  6.      return fib_tail(0, 0, 1)  

Some explanation of the 1-1 conversion process:

#1. We need a helper function, `fib_tail` to keep track of the variables we update in the while loop. (lines 4-5 in iterative)

#2-3. Return `curr` when the opposite of the while condition is met. (lines 3,6 in iterative)

#4. Recursively call `fib_tail`, using same update logic as while loop body when passing arguments. (line 5 in iterative)

#5. Call helper function with initial values for the additional variables (line 1 in iterative)

* We're going to pretend that Python supports tail recursion. It doesn't, but I figure more people are familiar with python; think of it more as pseudocode for instruction. You could easily implement the above in something like Scheme