We begin by discussing the connection between the ABC conjecture and
Szpiro's conjectural relationship between the conductor and
discriminant of an elliptic curve. Then we discuss a conjecture of
Lang which predicts, in particular, that among all elliptic curves

over

and all rational points

in

, there is a point of
smallest nonzero canonical height. After giving some computational
examples due to William Stein, we will then discuss a theorem of
Hindry and Silverman which implies that Lang's conjecture is implied
by Szpiro's (and hence by the ABC) conjecture.