This chapter provides a theoretical underpinning for careers advisers’work with clients. It draws on theories of both counselling and occupational guidance and shows how a skilled practitioner can draw upon both of these sources to enhance her understanding of inner conflicts and external influences which may affect a client’s outlook on life and ability to make rational, well-founded career decisions. Theoretical knowledge can enable a careers adviser to work in a more informed and therefore less reactive way to her observations of her client’s behaviour. We shall consider some counselling theories which inform all helping relationships, then go on to indicate a range of factors which may influence a client, finishing with a brief look at the community interaction theory of occupational guidance developed by Bill Law.