Without any doubt, phase-locked loops (PLLs) are the most popular and widely used technique for the synchronization purposes in the power and energy areas. They are also popular for the selective extraction of fundamental and harmonic/disturbance components of the grid voltage and current. Like most of the control algorithms, designing PLLs involves a tradeoff between the accuracy and dynamic response, and improving this tradeoff is what recent research efforts have focused on. These efforts are often based on designing advanced filters and using them as a preprocessing tool before the PLL input. A filtering technique that has received a little attention for this purpose is the least-error squares (LES)-based filter. In this paper, an adaptive LES filter-based PLL, briefly called the LES-PLL, for the synchronization and signal decomposition purposes is presented. The proposed LES filter can be understood as an adaptive complex-coefficient filter because its implementation involves cross couplings between orthogonal axes. The stability of designed LES-PLL is analyzed by the derivation of its small-signal model. Some control design guidelines are also presented. The effectiveness of proposed PLL structure is finally evaluated using experimental results.