Books are an excellent resource for gaining knowledge and understanding various subjects. When it comes to preparing for the UPSC (Union Public Service Commission) exam, it is crucial to refer to the right books as references. Here are some recommended books that can serve as valuable resources for UPSC preparation:

1. History:
- "India's Struggle for Independence" by Bipan Chandra: This book provides a comprehensive account of India's freedom struggle.
- "History of Modern India" by Rajiv Ahir: It covers important events from the mid-18th century to the present day.

2. Geography:
- "Certificate Physical and Human Geography" by Goh Cheng Leong: This book covers both physical and human geography in detail.
- "Oxford School Atlas" by Oxford University Press: It provides updated and accurate maps for better understanding of geographical concepts.

3. Polity:
- "Indian Polity" by M. Laxmikanth: It is a comprehensive guide to the Indian political system, including the Constitution and governance.
- "Introduction to the Constitution of India" by D.D. Basu: This book provides an in-depth analysis of the Indian Constitution.

4. Economy:
- "Indian Economy" by Ramesh Singh: It covers various aspects of the Indian economy, including economic development, planning, and current issues.
- "Economic Survey" by the Government of India: This annual publication provides insights into the country's economic performance and policy measures.

5. Science and Technology:
- "Science and Technology in India" by Spectrum Publications: It covers the developments in science and technology in India.
- "General Science for Civil Services Preliminary Examination" by Tata McGraw Hill: This book covers basic science concepts relevant to the UPSC exam.

6. Current Affairs:
- "The Hindu" or "The Indian Express" newspapers: Reading these newspapers regularly will help in staying updated with current affairs and news.
- "India Year Book" by the Publications Division: It provides a comprehensive overview of government schemes, policies, and initiatives.

Remember, while these books are highly recommended, it is also important to refer to NCERT (National Council of Educational Research and Training) textbooks from classes 6 to 12 for a strong foundation in various subjects.

In conclusion, the above-mentioned books can serve as excellent references for UPSC preparation. However, it is important to supplement your reading with current affairs magazines, online resources, and previous years' question papers for a well-rounded preparation strategy.