This special issue collects 9 peer-reviewed papers. The main topics deal with smart wearable device development (4 papers) and intelligent signal processing algorithms integrated into wearable devices (5 papers). These papers are based on specific applications on online monitoring or tracking of human physical activity (5 papers) and medical indices (EEG, ECG, PPG and blood glucose) (4 papers) but can also be extended to processing of more generalized scenarios.