There are four basic food groups: milk chocolate, dark chocolate, white chocolate and chocolate truffles.

You therefore can count on a square meal (of the chocolate box sort) when the fourth annual Chocolate Festival opens tonight, October 5, with a preview party at Featherstone Center for the Arts on Barnes Road in Oak Bluffs.

The Art of Chocolate by Artists opens from 7 to 9 p.m. Donors to Featherstone’s Chocolate Festival will be treated to an evening of champagne and chocolates, at donor levels of $25, $50 and $100. In her tenure as Featherstone’s executive director, Francine Kelly has seen this event evolve into one of the more festive fundraising experiences on the Island. Patrons rave about the chocolate martinis and the spectacular truffles. They savor the variety of chocolates on offer.

The public is invited to sample chocolate-lovers’ favorite treats from noon to 4 p.m. on Saturday through Monday, Oct. 6 to 8. Chocolate cakes, candy, brownies and truffles will be available for tasting — $5 for three tastes. Milk chocolate is available. Dark chocolate fans will not be disappointed. And there is that unique white chocolate connoisseur who will be thrilled at the delectable samples.

The annual Chocolate Festival also features an educational component with the story of chocolate told in photo and film. The art of chocolate will be on display as imagined by various Vineyard artists. And certified chocoholics will be there to share their knowledge and hints at tempering the finest chocolates on the Vineyard.

For details, call Featherstone at 508-693-1850. Featherstone is on Barnes Road in Oak Bluffs.