Imre Z. Ruzsa (born 23 July 1953) is a Hungarian mathematician specializing in number theory.

Since then he has been at the Alfréd Rényi Institute of Mathematics of the Hungarian Academy of Sciences.

He proved that an essential component has at least (log x)1+ε elements up to x, for some ε > 0.

On the other hand, for every ε > 0 there is an essential component that has at most (log x)1+ε elements up to x, for every x.

Ruzsa also showed the existence of a Sidon sequence which has at least x0.41 elements up to x.