  A set $C$ of vertices in a graph $G=(V,E)$ is an identifying code if it is
dominating and any two vertices of $V$ are dominated by distinct sets of
codewords. This paper presents a survey of Iiro Honkala's contributions to the
study of identifying codes with respect to several aspects: complexity of
computing an identifying code, combinatorics in binary Hamming spaces, infinite
grids, relationships between identifying codes and usual parameters in graphs,
structural properties of graphs admitting identifying codes, and number of
optimal identifying codes.
