<p>Indian summer monsoon (ISM) is a seasonal phenomenon determined by the radiant energy absorbed from the sun and the ability of water vapor to rise in the atmosphere through tropospheric overturning circulation to maintain an equilibrium energy state. In the present-day climate, such a state is attained during the boreal summer, and June to September is considered the ‘monsoon season’ over India. Almost 4/5-th of the annual total rain over Indian land falls during this 1/3-rd part of a year. The growth of early civilization over this region was driven primarily by water availability on account of monsoon rainfall. The seasonal rainfall still significantly impacts the country’s agriculture, water resource management, and power generation. Most of the research on monsoon rainfall has primarily focused on two main areas: interannual variations of the seasonal total rainfall and its sub-seasonal variations, giving insights into the physical mechanisms associated with the aforementioned variations and their predictability. This study reviews the leading theories, key characteristics, and various applications of the Indian summer monsoon. Additionally, we highlight the advancements in monsoon predictability over the past few decades that led to a force-multiplier effect of a ratio of 1:50 and the ongoing efforts to enhance monsoon forecasts across various time scales.</p>