Unequal Error Protection (UEP) is the key to future prioritized data communication, multilevel qualities of service (QoSs), and scalable multimedia transmission. This means that these applications provide data of different importance and require different error protection. Under these conditions, multicarrier modulation is highly recommended due to its suitability for adapting individual sub-carriers, which are subject to different channel conditions, with different bit rates, code rates, and powers according to any given performance constraints.We propose a set of new UEP adaptive modulation schemes that allow for allocating an arbitrary number of bits with arbitrary noise margins or symbol error-ratios (SERs), thereby realizing UEP. In these schemes, the subcarriers are subdivided into smaller sets, where each set is dedicated to a certain priority class. These schemes are realized for single-input single-output (SISO) and multiple-input multiple-output (MIMO) transmission methods under different channel conditions. Finally, we consider the same bit-loading and channel adaptation techniques for multiuser systems to devote different QoSs across a given number of users.