The paper analyses in a systematic manner these structural factors of
interfaces in relation to their properties that constitute the backgro
und of ''interface engineering''. It is shown that the specific proper
ties of interfaces are related to their structure. A brief description
of recent structural models of interfaces is therefore presented. A n
ew concept of interface microstructure composed of different kinds of
interfacial defects is introduced and their role in determining the in
terface properties is emphasised. It is shown that interfaces control
the processes taking place in the material under external solicitation
s or during the microstructure formation, mainly through their interac
tion with other crystal defects. Various examples illustrating the pos
sibility of controlling and improving the material properties by appro
priate changes of interface structures are presented in the case of me
tals, alloys, intermetallics and ceramics.