Capital structure theory is central to the formulation of financing plans and the implementation of financing decisions by firms, and has been a hot topic of research in the financial world. According to Modigliani and Miller (1958), it does not matter if a company is financed by equity or debt under perfect market condition. However, other capital structure theories (trade-off theory and pecking order theory) emerged in an attempt to explain firms financing decision. This report conducts a literature review and critically analyses and evaluates five capital structure theories by outlining each of them. These include Modigliani and Miller's 1958 and 1963 theories, trade-off theory, pecking order theory, and risk and return. In addition, this report discusses the usefulness of these five theories for the financing decisions of firms.