Last night marked the start of acceptably timed Halloween parties, and, predictably, costume enthusiasts were out in full force. In L.A., Katy Perry attended Kate Hudson’s annual Halloween bash dressed as a Cheeto, while back in New York, Peter Brant Jr. threw a costume party in the guise of a spritely Dionysus. Across town, Madonna and Aretha Franklin forwent dressing up and attended Alicia Keys’s annual Black Ball benefiting Keep a Child Alive, while the fashion set — including Hilary Rhoda, Leandra Medine, Giovanna Battaglia, and also Jennifer Connelly — showed up at Dolce & Gabbana’s Artwalk NY benefit. On Wednesday, Rihanna chatted with Tom Ford while wearing confetti pasties (designed by him) at the amfAR gala in L.A., while back in New York, Kanye ventured to Brooklyn Bridge Park to attend the + Pool Fall Swim Benefit. Meanwhile, Madewell celebrated their Williamsburg store opening with Cory Kennedy and Fiona Byrne, Jared Leto hung out with Alessandra Ambrosio at the Rimowa opening party in New York, and Jessica Seinfeld celebrated the launch of the Baby Buggy Stuart Weitzman capsule. Click through the slideshow for these and more highlights from the week’s biggest parties.