Let \(\mathcal{X }\) be a set of outcomes, and let \(\mathcal{I }\) be an infinite indexing set. This paper shows that any separable, permutation-invariant preference order \((\succcurlyeq )\) on \(\mathcal{X }^\mathcal{I }\) admits an additive representation. That is: there exists a linearly ordered abelian group \(\mathcal{R }\) and a ‘utility function’ \(u:\mathcal{X }{{\longrightarrow }}\mathcal{R }\) such that, for any \(\mathbf{x},\mathbf{y}\in \mathcal{X }^\mathcal{I }\) which differ in only finitely many coordinates, we have \(\mathbf{x}\succcurlyeq \mathbf{y}\) if and only if \(\sum _{i\in \mathcal{I }} \left[u(x_i)-u(y_i)\right]\ge 0\). Importantly, and unlike almost all previous work on additive representations, this result does not require any Archimedean or continuity condition. If \((\succcurlyeq )\) also satisfies a weak continuity condition, then the paper shows that, for any\(\mathbf{x},\mathbf{y}\in \mathcal{X }^\mathcal{I }\), we have \(\mathbf{x}\succcurlyeq \mathbf{y}\) if and only if \({}^*\!\sum _{i\in \mathcal{I }} u(x_i)\ge {}^*\!\sum _{i\in \mathcal{I }}u(y_i)\). Here, \({}^*\!\sum _{i\in \mathcal{I }} u(x_i)\) represents a nonstandard sum, taking values in a linearly ordered abelian group \({}^*\!\mathcal{R }\), which is an ultrapower extension of \(\mathcal{R }\). The paper also discusses several applications of these results, including infinite-horizon intertemporal choice, choice under uncertainty, variable-population social choice and games with infinite strategy spaces.