Single Leptoquark Production

The single production of leptoquarks in $e^+e^-$, $e\gamma$ and $\gamma \gamma$ linear colliders is discussed. We show that these new particles could be seen in such machines even if their mass is close to the kinematic limit. (Invited talk given by G.B. at the ``Workshop on Physics and Experiments at Linear $e^+e^-$ Colliders'', Waikoloa, Hawaii, April 26-30, 1993.)