Abstract: A size adjustable athletic boot of a molded plastic or composite construction which is adjustable in length, width and height allowing three dimensional fit (3-D fit) for a variety of foot sizes. The boot has a base section and a tongue section which extends from a toe end of the base section. The tongue and base sections combine to define a variable volume foot space between them. A heel section telescopes over a rear end of the base section. The heel section has a heel surface which in combination with an upper surface of the base section defines a foot support surface. A cuff extends upward from a heel wall of the heel section. The cuff and a free end of the tongue section confront one another and define a foot entry opening between them. An adjustment mechanism is adapted to selectively position the heel section on the rear end of the base section to vary the length of the foot support surface relative to the length of a user's foot.