- The Vedas and their interpretation
- The Indus-Sarasvati Civilisation
- The history and culture of ancient India
- Astronomy and cosmology
- Archaeoastronomy
- Linguistics
- Philosophy of science
- Education
Some of his notable works include:
- The Vedas and the Indus-Sarasvati Civilisation (1995)
- Indus-Sarasvati Civilisation: A New Perspective (2001)
- The Astronomical Code of the Rigveda (2002)
- The Rigveda: A Historical Analysis (2003)
- The Science of Ancient India (2007)
- In the Light of the Vedas: Recasting Indian History (2010)
- Vedas and the Cosmic Order (2014)
- The Language of the Gods: Recasting the Study of Ancient India (2019)
Kak's work has been praised by some scholars for its originality and insights, while others have criticized it for being speculative and lacking in empirical evidence. Nevertheless, there is no doubt that Kak is one of the most influential and controversial figures in the study of ancient India.