This book entitled "The Active Sun" presents an observational study of some dynamical phenomena in the solar atmosphere, their physical interpretations, and consequences. This book deals with both space-borne and ground-based observations at multiwavelength (Visible, EUV, X-ray, Radio) to address various scientific issues. The book contains the investigations of the novel observations of the multiple MHD wave harmonics (fast kink, slow-acoustic) in various types of magnetic flux-tubes in the solar atmosphere at small (X-ray bright point loops) and large (prominence, coronal hole)to diagnose the localized plasma conditions. In addition to the study of observations of multiple wave harmonics and their diagnostic capability under the frame-work of the MHD seismology, this book also contains the study of an M-class flare and associated dynamical plasma processes and eruptions at multiwavelength.
