This review article is concerned with basic aspects and some selected topics in photonic crystal (PhC) devices. It starts with a significantly historical aspect of basic principles for photonic crystals that it is hoped will help the reader to develop a critical appreciation of the research literature. It continues by describing topics such as PhC beamsplitters, slow-light structures, micro-/nanoresonators, coupled resonator optical waveguides (CROWs) and PhC-based semiconductor lasers. Emphasis is placed on both the conceptual and the practical matters that need to be addressed in order to fulfill the tasks of designing and realizing devices that exploit photonic crystal principles. The review also addresses some of the problems encountered in the fabrication of photonic crystal devices using the planar technologies of integrated photonics, which are those that are most likely to be used in future commercial production.