The paper initially reviews major issues of slope instability at active volcanoes on the basis of geotechnical and engineering geology literature. A detailed discussion is then provided with reference to two case studies on Italian insular active volcanoes: Stromboli and La Fossa (Vulcano Island). At Stromboli, the role of magma intrusion in initiating the instability phenomena associated to major eruptions and the particular mechanical behaviour of the volcaniclastic deposits in controlling the 2002 submarine failure are investigated by means of numerical and conceptual models based on an extensive geotechnical characterization. At La Fossa, the influence of flank erosion, hydrothermal alteration, and anomalous pore pressures produced by hydrothermal activity on the evolution of the NE sector of the volcanic edifice are described with the aid of numerical analyses based on laboratory and in situ investigations.