Volcanic tremor is a common type of seismicity associated with active volcanoes. Its key distinguishing features are the emergent character and the long duration compared with earthquake-generated signals. Most probably, volcanic tremors are caused by processes related to degassing of magmas or molten rocks. The physical mechanism of volcanic tremors remains the subject of considerable debate. Therefore any case study could be useful to improve our understanding of this phenomenon. The objective of my thesis is to analyze volcanic tremor evolution for significant time period and to link this type of seismicity with magmatic processes under volcanoes. In particular, I will analyze seismic observation collected on volcanoes in the Kamchatka peninsular, Russia. Kamchatka is a natural laboratory to study volcanic processes because of the presence of several active volcanoes with various ages, chemical compositions, and eruptive types. I my work I will use the data of permanent seismic station of the Kamchatka volcano-monitoring network and those from a few temporary seismological experiment performed during recent years.