We discuss the strong-coupling expansion in Euclidean field theory. In a formal representation for the Schwinger functional, we treat the off-diagonal terms of the Gaussian factor as a perturbation about the remaining terms of the functional integral. In this way, we develop a perturbative expansion around the ultra-local model, where fields defined at different points of Euclidean space are decoupled. We first study the strong-coupling expansion in the (λϕ 4 ) d theory and also quantum electrodynamics. Assuming the ultra-local approximation, we examine the singularities of these perturbative expansions, analysing the analytic structure of the zerodimensional generating functions in the complex coupling constants plane. Second, we discuss the ultra-local generating functional in two idealized field theory models defined by the following interaction Lagrangians: L II (g 1 , g 2 ; ϕ) = g 1 ϕ p (x) + g 2 ϕ −p (x), and the sinh-Gordon model, i.e., L III (g 3 , g 4 ; ϕ) = g 3 (cosh(g 4 ϕ(x)) − 1). To control the divergences of the strong-coupling pertur-bative expansion two different steps are used throughout the paper. First, we introduce a lattice structure to give meaning to the ultra-local generating functional. Using an analytic regularization procedure we discuss briefly how it is possible to obtain a renormalized Schwinger functional associated with these scalar models, going beyond the ultra-local approximation without using a lattice regularization procedure. Using the strong-coupling perturbative expansion we show how it is possible to compute the renormalized vacuum energy of a self-interacting scalar field, going beyond the one-loop level.