Emotion perception is intrinsically subjective, and people usually perceive different emotions in the same song. This subjectivity issue makes the performance evaluation of an MER system fundamentally difficult because a common agreement on the classification result is hard to obtain. An MER system that neglects the subjectivity issue and assigns emotion labels or values to music pieces in a deterministic fashion cannot perform well in practice, since it is likely that a user is not satisfied with the prediction result. The following four chapters describe a number of methods that have been developed to address the subjectivity issue, including techniques for soft assignment and personalization. We begin with a fuzzy approach that is developed for categorical MER in this chapter. This approach estimates the likelihood of perceiving an emotion when listening to a music piece, thereby making the prediction result less deterministic.