Lord Ganesh, the patron deity is the God of wisdom. Come August and September, preparations to celebrate Ganesh Utsav - the favorable day when Lord Ganesh was born - begin with great enthusiasm throughout the state. The 11-day festival begins with the installation of beautifully sculpted Ganesh idols in homes and Pandals (large tents), colorfully decorated, depicting religious themes or current events. The Ganesh idols are worshiped with families and friends. Many cultural events are organized and people participate in them with great interest. After ten exciting days comes the time to say goodbye to the beloved God.
History of Ganesh Utsav

In 1893, Indian freedom fighter and social reformer Lokmanya Tilak transformed the annual domestic festival into a large, well-organized public event.

Tilak encouraged installation of large public images of Ganesh in pavilions, and also established the practice of submerging in rivers, sea, or other pools of water all public images of the deity on the tenth day after Ganesh Chaturthi.
Under Tilak's encouragement, the festival facilitated community participation and involvement in the form of intellectual discourses, poetry recitals, performances of plays, musical concerts, and folk dances. It served as a meeting ground for people of all castes and communities in times when, in order to exercise control over the population, the British discouraged social and political gatherings.
Ganesh Utsav Celebration
Two to three months prior to Ganesh Chaturthi, artistic clay models of Lord Ganesha are made for sale by specially skilled artisans. They are beautifully decorated & depict Lord Ganesh in various poses. The size of these statues may vary from 3/4 of an inch to over 25 feet.
Ganesh Chaturthi starts with the installation of these Ganesh statues in colorfully decorated homes and specially erected temporary structures mandapas (pandals) in every locality. The pandals are erected by the people or a specific society or locality or group by collecting monetary contributions. The pandals are decorated specially for the festival, either by using decorative items like flower garlands, lights, etc. or are theme based decorations, which depict religious themes or current events.

Ganesh Visarjan in Mumbai

The main sweet dish during the festival is the modak (modaka or modagam in South India). A modak is a dumpling made from rice flour/wheat flour with a stuffing of fresh or dry-grated coconut, jaggery, dry fruits and some other condiments. It is either steam-cooked or fried. Another popular sweet dish is the karanji (karjikai in Kannada) which is similar to the modak in composition and taste but has a semicircular shape.
Public celebrations of the festival are hugely popular, with local communities (mandalas) vying with each other to put up the biggest statue & the best pandal. The festival is also the time for cultural activities like singing and theater performances, orchestra and community activities like free medical checkup, blood donation camps, charity for the poor, etc.
Today, the Ganesh Festival is not only a popular festival, it has become a very critical and important economic activity for Maharashtra. Many artists, industries, and businesses survive on this mega-event. Ganesh Festival also provides a stage for budding artists to present their art to the public. The same holds true for Bangalore, Hyderabad and Chennai too. In Maharashtra, not only Hindus but many other religions also participate in the celibration of Ganesha festival like Muslims, Jains, Christian and others. This festival has managed to re-establish the unity among the Indians during British Era.
(from wikipedia)