Wavelength-domain tracking (WDT) is a new concept for application in multiple-beam optical storage systems. Tracking errors caused by use of multiple beams on curved tracks are avoided in WDT systems by optimizing separations of focused beam spots. The control of beam spot separations is accomplished by wavelength tuning of individual laser sources. Feasibility of WDT is demonstrated by implementation and testing of a single-beam WDT tracking servo. Also, a novel method of error signal extraction by low-frequency modulation is proposed.