What is the phase relationship between the current through and the voltage across a series resonant circuit at resonance?

At resonance in a series RLC circuit, the inductive reactance (which causes voltage to lead current) and the capacitive reactance (which causes voltage to lag current) are exactly equal in magnitude but opposite in phase. As a result, they cancel each other out completely. With the net reactance being zero, the circuit behaves as if it is purely resistive. In any purely resistive AC circuit, voltage and current are exactly in phase.