This thesis explores the question how unilateral conduct can create, vary or discharge obligations in English private law and how unilateral conduct is regulated. First, it is explained that the reason for asking this question follows from the candidate’s background in a civil law jurisdiction, in which unilateral juridical acts are regarded a category of legally relevant behaviour. After observing the obstacles in English law to the recognition of the civil law concept of unilateral juridical acts, a number of examples of unilateral conduct are identified that create legal effect. The focus of the thesis is on examples of unilateral conduct that create, vary or discharge obligations. English law allows the creation of obligations by unilateral conduct only in very specific instances. It is observed that unilateral conduct can create or transfer property rights. The different approach is explained primarily by deeply rooted distinction in English law between words and acts. Subsequently, the thesis discusses how unilateral conduct is regulated. For some issues, notably interpretation, revocability and the intention to create legal effect, similar rules apply to the different examples of unilateral conduct. For other issues, especially mistake and form requirements, the rules diverge. It is concluded that unilateral conduct forms a category of legally relevant behaviour in English law. This category is divided in unilateral conduct that creates obligations, quasi-contractual unilateral conduct that varies or discharges obligations and unilateral voluntary property transactions. Whereas quasi-contractual unilateral conduct is closely related to contracts and should thus generally be regulated in a manner similar to contracts, the unilateral voluntary property transaction is a distinct concept, to which specific rules apply.