A joint session of both the houses of parliament are called in case their is a disparity about a bill. If one house of indian parliament ie either the Lok Sabha or the Rajya Sabha refuses to pass a bill or does not give any decision on a bill while the other house has voted in favour to pass the bill a joint session is called.
The President of India has the power to summon a joint session of both the houses.
The Speaker of the Lok Sabha presides over a joint session of houses.
Usually in a joint session the will of the Lok Sabha prevails because it members are in majority ie about twice the number of members of Rajya Sabha. The members in Lok Sabha are approximately 545
Since the adoption of Indian Constitution only three bills have to be passed through a joint session. These are:-)
1. Dowry Prohibition Act (1961)
2. The Banking Service Commission Repeal Bill (1978)
3. The Prevention of Terrorist Activities Act (2002)