Why we celebrate
Anant Chaturdashi is the worship of Lord Vishnu in his infinite (Anant) form, and the day Ganesha idols are immersed (Visarjan).
Regional tradition
When
Anant Chaturdashi falls on the fourteenth day (Chaturdashi) of the bright fortnight of Bhadrapada (August-September), the tenth day of Ganesh Chaturthi.
Since when it is followed
The Ananta vrata and the Ganesha Visarjan on this day have been observed for centuries.
Regional tradition
Who celebrates / for whom
Celebrated by Hindus, especially in Maharashtra where Ganesha idols are immersed.
Origin
The origin is the worship of Lord Vishnu as Ananta (the infinite) and the concluding day of Ganesh Chaturthi.
Regional tradition; Ganesh Chaturthi
Key deities
Lord Vishnu (Ananta form) and Lord Ganesha.
How to celebrate
Worship the Ananta sutra (a sacred thread with 14 knots), tie it on the arm, and in Maharashtra perform the Ganesha Visarjan.
Rituals & offerings
Ananta puja, tying of the Ananta sutra, and Ganesha Visarjan.