**1. Introduction**

The human tremor is one of the most common movement disorders, which is characterized by repetitive and stereotyped movements. The origins of tremor are still not clear, however tremor can be associated with physiological phenomena, such as ageing, and with neurological disorders, for instance, Parkinson's disease. The first type of tremor is referred to as physiological tremor, whereas the latter as pathological tremor.

The clinical evaluation of tremor can be a valuable tool for the diagnosis of neuromuscular disorders and also for monitoring their progress. However, in a number of circumstances the discrimination between physiological and pathological tremor may not be clinically evident. In this context, the use of sensors for detecting tremor, and the data analysis tools employed in its quantification and classification are of paramount importance.

In this chapter, the origins, detection and quantification of tremor are discussed. The chapter begins with a review concerning the definition and classification of distinct types of tremor. A review of current theories that explain the origins of tremor are presented. The problem of detecting tremor by using electronic devices is addressed, and new advances in the area of tremor detection are introduced. A review and a critical discussion of the most common tools employed for tremor quantification and classification is provided. The chapter finishes by pointing out key unanswered questions in tremor research.
