The Portfolio Investment Scheme (PIS) allows registered Foreign Institutional Investors (FIIs) and Non-Resident Indians (NRIs) to buy and sell shares and convertible debentures of Indian companies. FIIs must be registered with SEBI and obtain permission from the RBI through a designated bank. They can purchase securities through registered brokers on recognized stock exchanges. The payment must be made through inward remittance or funds held in an authorized dealer's account. The ceiling for overall investment for FIIs is 24 percent of the paid up capital of the Indian company and 10 percent for NRIs/PIOs. NRIs can invest under the PIS through designated branches, with limits on the paid-up value of shares and debentures.