The Durga Puja festival, held in accordance to the lunar calendar of Bangabda around the first week of October, is the most vibrant time in Kolkata. This Hindu religious festival commemorates the mythology of Goddess Durga and her trusty lion steed overpowering and killing the demon Mahishasura (Buffalo-demon). The first ceremony takes place on Mahalaya, the day the Goddess was conceived, and ends on Bijaya Dashami (the victorious tenth day), the day the Goddess finally kills the demon in battle. Puja is performed only on the sixth to the tenth day. Kolkata celebrates Durga Puja with elaborate pandal—temporary decorative scaffolding serving the purpose of a temple—constructions on virtually every street. Crowds of people throng the streets of Kolkata all night; the number is purported to be a few million on the climactic eighth and ninth nights, possibly the second largest annual human conglomerate after the Hajj. On this festival, there is a practice of giving gifts—usually new clothes in the latest fashion in pre-puja get-togethers, and sweets at post-puja get-togethers (Bijaya Sammelani). The festival is commemorated by the publishing of Annuals (Sharadiya or Puja Annual) by most Kolkata magazines and presses.
Today's Puja goes far beyond religion. In fact, visiting the pandals recent years, one can only say that Durgapuja the largest outdoor art festival on earth. In the 1990s, a preponderance of architectural models came up on the pandal exteriors, but today the art motif extends to elaborate interiors, executed by trained artists, with consistent stylistic elements, carefully executed and bearing the name of the artist.
At the end of the six days long festival, the idol is taken in a procession amid loud chants and drumbeats to the river or other water body, and it is cast in the waters symbolic of the departure of the deity to her home with her husband in the Himalayas. After this, in a tradition called Vijaya Dashami, families visit each other and sweetmeats are offered to visitors (Dashami is literally tenth day and Vijay is victory).
Saraswati Puja—the puja of the Goddess of Learning, Saraswati—is celebrated with domestic pujas, and familial gatherings in Kolkata. The typical fare (bhog) which accompanies the Puja depends dramatically on whether the family is initially from West Bengal (or ghoti) or from East Bengal—now Bangladesh—(or bangal). Ghotis have vegetarian fare, while bangals partake paired Hilsa fishes. Idols for these and other Pujas are made in the famous potters' district of Kumartuli. In Bengal, during Saraswati Puja, students celebrate the Homecoming of the Goddess of Learning. Books are often worshipped in lieu of the clay image of the Goddess. The puja is especially celebrated in schools and other educational institutes. And gives an opportunity of free-mixing among school children. This is the equivalent of Valentine's Day to them.
Christmas was a big festival in Kolkata during the British Raj, but has slowly declined in importance since. The Anglo-Indian community still celebrates Christmas in a big way, with a huge service at St. Paul's Cathedral and with the Park Street restaurant district and New Market decked out on the 24th and 25th. The multicultural nature of Kolkata becomes apparent as the most sought after confectionaries during this time were from the British confectioners Flury's and Jewish confectioners Nahoum's.

The 'Calcutta Book Fair (or Kolkata Boi Mela) is unique and is the world's largest non-trade annual book fair. Held on the Maidan, this fair attracted over 600 stalls, selling over Rs. 18,00,00,000 (read as "18 crores") worth of books and attracting close to 150,000 visitors in 2005. Started in 1975 by the Publishers' and Booksellers' Guild, it has rapidly become one of the world's leading book fairs. It has a Monmarte with budding poets and artists, an annual theme country with authors like Günter Grass and Richard Dawkins visiting the fair as chief guests, a fairground experience complete with candyfloss and hawkers, but most importantly, it provides a place to view more than a million new and used book titles at one go—a larger book conglomerate than any Barnes & Noble or Borders superstore. It starts on the last Wednesday of January, and continues for twelve days, including two weekends.
Website of the Kolkata International Film Festival
is an annual event (first week of June)organised by Kolkata [Eso Natak Shikhi][www.calcuttayellowpages.com/adver/103336.html], a Kolkata based group theatre working with children since 1990. Teams from all over India & abroad participate & perform at Rabindra Sadan. The fest is assisted by Ministy of Culture & Information, Government of West Bengal. Ministry of Transport & Sports, Government of West Bengal. Eastern Zonal Cultural Centre, Ministry of Tourism & Culture, Govt. of India.