Smart contracts are event-driven computer programs used to automatically execute all or parts of the agreements between two or more entities, pursuant to their specifications. The self-executing and self-enforcing attributes of smart contracts present numerous potential benefits, such as cost efficiency, accuracy, and reliability, as well as the potential to support several sustainable development goals. Smart contracts can be very efficient in many sectors, with important automation, procurement, financial, and other supply chain management features. For this study, a systematic literature review was performed, with a view to assessing, synthesizing, and critique the current state of legal and security aspects of smart contracts. The analysis of publications and reports gathered allowed the identification and mapping of the most relevant aspects and revealed numerous issues and vulnerabilities associated with the use of this technology. This paper provides the following contributions: the study and organization of a large corpus of relevant publications; the review of smart contract definitions, from several perspectives; an outline of smart contract characteristics; a framework for effective smart contracting, addressing legal and security issues and proposing several improvements.