A microcatheter system is disclosed which may include a microcatheter, one or more microcatheter extensions, and/or a microcatheter hub. In an embodiment, the microcatheter has a plurality of zones where the outside diameter of each zone from the distal to the proximal end has an outside diameter that is the same as or greater than the previous zone while the inside diameter is constant throughout the microcatheter length. In a further embodiment, a unique joining mechanism is employed for coupling a microcatheter to a microcatheter extension or to a microcatheter hub.
