A highly reconfigurable and switchable quadrature coupler with simultaneous control in terms of operating frequency, coupling ratio, and coupling direction is presented. To start with, a prototype coupler based on an ideal admittance-inverter model is investigated, and a method to obtain the admittance-inverter values for an arbitrary coupling ratio is described. Next, a tunable-admittance-inverter network implemented with lumped inductors and varactors, which features reconfigurable operating frequency, and tunable-admittance-inverter value is discussed. The conceived reconfigurable coupler is then realized by replacing the ideal admittance inverters with the proposed tunable-admittance-inverter circuit to provide it with operating-frequency and coupling-ratio controllability. Furthermore, when exchanging the admittance-inverter values in the coupler, the coupling direction is switched from forward to backward. The proposed technique is further developed into a general design procedure for reconfigurable-coupler implementations with an arbitrary admittance-inverter-based network. Wilkinson power dividers with equal and unequal power-division ratios are also shown as examples. For experimental/demonstration purposes, a reconfigurable coupler prototype is fabricated and characterized. It demonstrates a tunable operating frequency from 1 to 1.5 GHz, a controllable power-division ratio between output ports from 1 to 0.7, and switchable operational direction between forward and backward.