A survey is given of Computer algebra systems, with emphasis on design and implementation aspects, by presenting a review of the development of ideas and methods in a historical perspective, by us considered as instrumental for a better understanding of the rich diversity of now available facilities. We first indicate which classes of mathematical expressions can be stated and manipulated in different systems before we touch on different general aspects of usage, design and implementation, such as language design, encoding, dynamic storage allocation and a symbolic-numeric interface. Then we discuss polynomial and rational function systems, by describing ALTRAN and SAC-2. This is followed by a comparison of some of the features of MATHLAB-68, SYMBAL and FORMAC, which are pretended general purpose systems. Before considering giants (MACSYMA and SCRATCHPAD) and gnomes (muMATH-79), we give the main characteristics of TRIGMAN, CAMAL and REDUCE, systems we tend to consider as grown out special purpose facilities. Finally we mention some modern algebra systems (CAYLEY and CAMAC-79) in relation to recent proposals for a language for computational algebra. We conclude by stipulating the importance of documentation.