Different maximum power point tracking (MPPT) techniques used in photovoltaic (PV) systems are evaluated based on several criteria such as simplicity, speed, and accuracy. There are tradeoffs among these criteria, and generally higher accuracy is achieved at the expense of speed and simplicity. This article aims to introduce Spline-MPPT technique as a fast, accurate, and uncomplicated method to find the maximum power point of PV systems under uniform irradiance and partial shading condition (PSC) in which characteristics of the PV string are distorted. The proposed method is based on cubic spline interpolation that defines an approximate function for a few sample points. Several interpolation-based methods have been proposed in the literature to find MPP under uniform irradiance. They, however, are incapable of finding the global maximum power point (GMPP) under partial shading conditions. The Spline-MPPT technique only uses a small number of current and voltage samples to estimate the MPP of the system and maintain on this point as long as environmental conditions remain unchanged. Simulation results attest to the superiority of the proposed method.