The authors study optimal tracking performance issues pertaining to finite-dimensional, linear, time-invariant feedback control systems. The problem under consideration amounts to determining the maximal tracking accuracy, or the minimal tracking error between the output and the reference signals of a feedback system, attainable by all possible stabilizing compensators under either a unity feedback structure or a two-parameter structure. The tracking error is defined in the \(\mathcal L_2\) sense using an integral square error criterion, and the reference signals under consideration are step signals. It is shown that plant nonminimum phase zeros have a negative effect on a feedback system's ability to reduce the tracking error, and that in a multivariable system this effect results in a way depending on not only the zero locations, but also the zero directions. If a unity feedback structure is used for tracking purposes, plant nonminimum phase zeros and unstable poles can together play a particularly detrimental role in the achievable tracking performance, especially when the zeros and poles are nearby and their directions are closely aligned. On the other hand, if a two-parameter controller structure is used, the achievable tracking performance depends only on the plant nonminimum phase zeros.