Abstract. A number of useful bivariate spline methods are global in nature, i.e., all of the coefficients of an approximating spline must be computed at one time. Typically this involves solving a system of linear equations. Examples include several well-known methods for fitting scattered data, such as the minimal energy, least-squares, and penalized least-squares methods. Finite-element methods for solving boundary-value problems are also of this type. It is shown here that these types of globally-defined splines can be efficiently computed, provided we work with spline spaces with stable local minimal determining sets. §1. Introduction Bivariate splines defined over triangulations are important tools in several application areas including scattered data fitting and the numerical solution of boundaryvalue problems by the finite element method. Methods for computing spline approximations fall into two classes: 1) Local methods, where the coefficients of the spline are computed one at a time or in small groups, 2) Global methods, where all of the coefficients of the spline have to be computed simultaneously, usually as the solution of a single linear system of equations.In this paper we focus on global methods, and in particular those that arise from minimizing a quadratic form, possibly with some constraints. The purpose of this paper is to show how such minimization problems can be efficiently solved for spline spaces that possess stable local minimal determining sets (see Sect. 2). In particular, we show how our approach applies to three commmonly used scattered data fitting methods: the minimal energy method, the discrete least-squares method, and the penalized least-squares method. In addition, we discuss how it works for solving boundary-value problems involving partial differential equations. The standard approach to solving global variational problems involving piecewise polynomials on triangulations is to use Lagrange multipliers to enforce interpolation and smoothness conditions, see Remark 1. This results in a linear system