This chapter discusses the difficult questions surrounding treaties in Canadian constitutional law. The first part examines treaty-making powers, in particular, the lack of explicit constitutional provisions which outline how, and who, may enter into treaties under Canadian federalism. Under the current Canadian modus vivendi the federal government is the entity which exercises foreign relations, including treaty-making. However, Canadian foreign relations are rich and complex, and all provinces engage in some way in foreign relations—with Ottawa’s explicit or tacit consent—particularly through the use of administrative agreements. The second part of this chapter examines treaty implementation in Canada, which must occur according to the usual division of powers under the Constitution Act, 1867 following the Labour Conventions Reference. Moreover, under current law there are at least 13 forms of implementation—meaning that “legislative implementation” will not always be necessary for a treaty to be considered “implemented” under Canadian law.