This two-volume textbook provides comprehensive coverage of partial differential equations, spanning elliptic, parabolic, and hyperbolic types in two and several variables. In this first volume, special emphasis is placed on geometric and complex variable methods involving integral representations. The following topics are treated, integration and differentiation on manifolds, foundations of functional analysis, Brouwer's mapping degree, generalized analytic functions, potential theory and spherical harmonics, and linear partial differential equations.