The paper proposes a possible method for further developing the theory of the firm in a generalised way. It argues that a more general theory of the firm, called multidimensional theory of the firm, has to be built upon more realistic behavioural assumptions. As such an assumption, the Misesian human action concept is proposed, whose main advantage is that — as an integrated action — it encompasses both the calculative and the entrepreneurial elements in human behaviour. Four dimensions are established, the first three (core, market, entrepreneurial dimensions) represent the essential components of content for the understanding of the firm, and the fourth one (time dimension) makes it possible to consider the firm as something operating in real time. It is also shown how these dimensions are interconnected.