It begins with a review of the basic principles of an electronic nose and explores possible ways in which the detection limit of conventional electronic nose technology can be reduced to the level required for the trace levels observed for many explosive materials. Next are reviews of the use of several different types of solid-state chemical sensors: polymer-based sensors, i.e. chemiluminescent, fluorescent and optical, to detect explosive materials; metal oxide semiconducting resistive sensors; and then electrochemical sensors. Next, different pattern recognition techniques are presented to enhance the performance of chemical sensors. Then biological systems are considered as a possible blue-print for chemical sensing. The biology can be employed either to understand the way insects locate odorant sources, or to understand the signal processing neural pathways. Next is a discussion of some of the new types of electronic noses; namely, a fast GC column with a SAW detector and a micromechanical sensor. Finally, the important issues of sampling technologies and the design of the microfluidic systems are considered. In particular, the use of pre-concentrators and solid phase micro extractors to boost the vapour concentration before it is introduced to the chemical sensor or electronic nose.