Summons and discovery powers enable tax authorities to compel attendance, inspection and production of documents, subject to retention limits and approval. Section 131 empowers specified income tax authorities to exercise civil court powers of discovery, inspection, compelling attendance and production of books and documents, and issuing commissions. These powers can be used even when no proceedings are pending. Authorities may impound produced books or documents after recording reasons, retain them for a limited statutory period, and seek senior supervisory approval to extend retention beyond that period.