An array is defined as a set of sensors, for example antennas or acoustic transducers. The outputs from these sensors can be processed in an adaptive manner to respond to an unknown interference environment in an attempt to optimise the performance of the system in some defined manner. The paper is intended as an introduction to, and to some extent a survey of, some of the methods used in adaptive array processing. It has, however, no pretence to be comprehensive. Some of the topics covered include the use of constraints, gradient techniques, including the stochastic steepest-descent algorithm, properties of the covariance matrix, the power inversion algorithm and the use of weight purturbation techniques.