Volcanoes are one of the most interesting and awesome geologic objects on the Earth. Studying volcanoes is important for several reasons. First of all, this is the question of safety of human life. Second, studying volcanoes gives us important information required for understanding the geologic processes occurring in the Earth’s interior. Third, volcanoes and associated hydrothermal systems can be important alternative sources of energy. In terms of geology and geophysics, one of the important goals in studying of volcanoes is to understand a structure of the crust and mantle beneath volcanoes. One of the effective tool is seismic tomography. But in the case of volcanoes, seismic tomography face the several problems related to limitations and physical constrains of particular methods. In this thesis, I argue that combining different types of geophysical and geological data (when possible) can be a good approach to solve the shortcomings of individual seismic tomography methods. Therefore, in this work I present results of combined utilizations and of joint inversions of different geophysical and geological data collected at following volcanoes: Anak Krakatau, Toba supervolcano (Indonesia), and Avachinsky (Kamchatka, Russia). I show that combining and/or jointly inverting different data types is a powerful tool that provides us with most reliable information about the structure of the crust beneath corresponding volcanoes.