Among the geophysical techniques used to monitor volcanic unrest, only gravimetry can supply direct information on changes in the distribution of underground mass over time and can thus provide unique insight into processes such as magma accumulation in void space or gas segregation at shallow depths. Despite its great potential, time-variable volcano gravimetry is not widely adopted, mainly due to (i) the high cost of instrumentation and (ii) the challenge in assessing the relatively small volcano-related gravity changes against unfavorable environmental conditions. Nonetheless, past studies have highlighted the value of time-lapse and continuous gravity observation for characterizing hazards, as well as improving our understanding of how volcanoes work. In this chapter a comprehensive technical, methodological and scientific insight is provided into time-variable volcano gravimetry, highlighting the advantages and limits of the method, as well as the future directions which could broaden its application.