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Least-squares ﬁnite element methods are an attractive class of methods for the numerical solution of partial differential equations. They are motivated by the desire to recover, in general settings, the advantageous features of Rayleigh–Ritz methods such as the avoidance of discrete compatibility conditions and the production of symmetric and positive deﬁnite discrete systems. The methods are based on the minimization of convex functionals that are constructed from equation residuals. This paper focuses on theoretical and practical aspects of least-square ﬁnite element methods and includes discussions of what issues enter into their construction, analysis, and performance. It also includes a discussion of some open problems.