This chapter presents new and current techniques that are suitable for monitoring sweat rate. Public and private researchers have been looking at small and cost-effective wearable sensors for monitoring parameters of physiological interest. Like many wearable systems, sweat rate sensors are very complex devices since their reactive layer has to be exposed to the target sample in order for the reaction to occur. Sweat is excreted by two types of glands: eccrine and apocrine. Eccrine glands are smaller than apocrine and are embedded in the dermis, that is, the layer of connective tissue lying under the epidermis. One of the main reasons for the fast development of wearable sensors is due to their high demand in sectors such as sports, fitness, and clinical medicine. Several devices are often used to provide information about the training session, for example, heart rate or electrocardiogram (ECG).