This weekend, Somerville's own HONK! Festival of Activist Street Bands marches (dances) its way back into our hearts (ears). Whether you've been every year for the past decade, or never heard about it, here's what you need to know:

What is it?

A brass band block party. A giant jam session. Somerville’s best invention.

Every October, mobile street bands from around the world descend on Somerville’s Davis Square, transforming it into a joyous, thumping musical hive. The bands are unplugged, the music is deafening and the audience is invited to dance and sing along.

The Second Line Social Aid & Pleasure Society Brass Band founded the HONK! Festival of Activist Street Bands in 2006 with the aim of bringing together like-minded groups from around the country. The event has since expanded into a three-day-long extravaganza and helped launch a movement, with similar festivals popping up in cities as near as Providence and as far as Rio de Janeiro. For many bands, lefty causes are de rigueur. If you’ve gone to a protest in the last year, chances are you saw — or at least heard — a honk band. (Due to HONK!'s popularity, "honk band" has come to refer to the particular style of mobile brass band featured at the festival.) But the HONK! Festival plays host to bands of many persuasions, from New Orleans second line outfits to Balkan brass ensembles to Haitian rara groups.

When and where is it?

HONK! begins on Friday, Oct. 6, in Somerville’s Hodgkins Park with a lantern workshop (starting at 4 p.m.) and parade (starting at 7 p.m.). Later that night, there are free concerts at ONCE Somerville and Aeronaut Brewing Co.

Saturday, Oct. 7, is the festival in Davis Square from noon to 9 p.m. This year there are 25 bands. Check out the full schedule here.

Sunday, Oct. 8, begins with a parade (noon to 2 p.m.) from Davis Square to Harvard Square, where the bands link up with Oktoberfest and perform on the main stage throughout the afternoon.

What should I wear? Should I bring my trumpet?

Dress for the weather and your own comfort. But if you’re inclined toward loud colors, glitter or costumes of any kind, you will not look out of place at HONK! The etiquette around joining in with the music varies from band to band, but I’d wager if you showed up with an instrument you wouldn’t have a hard time finding people who want to jam.

What do I have to be there for?

Frankly, I think the best way to enjoy HONK! is to wander around Davis Square on Saturday and let serendipity lead the way. But there are a few bands that I’m especially looking forward to. Check out my top picks below:

The Party Band

Saturday set times: 3 p.m. at Statue Park; 8 p.m. at Davis Square Plaza

Massachusetts is home to dozens of honk bands, and The Party Band from Lowell is one of the very best. I’ve caught them busking in Somerville on a few occasions. This sprawling group of first-rate musicians is utterly infectious.

New Creations

Saturday set times: 5 p.m. at Chester Street; 8 p.m. at Statue Park

New Orleans is home to one of the richest living brass band traditions, and HONK! usually features at least one band hailing from the Big Easy. This year it’s New Creations, a deeply funky outfit that has attended the festival several times in the past.

Rara Bel Poze

Saturday set times: 2 p.m. in Davis Square Plaza; 7 pm at Kenney Park

Rara is a street music tradition from Haiti that employs trumpet-like instruments made out of bamboo or salvaged metal, called vaksen, and a fleet of clattering percussion. This is the Boston-based Rara Bel Poze’s first time attending HONK!

What Cheer? Brigade

Saturday set times: 4 p.m. at the corner of Elm and Grove; 7 p.m. at 7 Hills Park

What Cheer? Brigade might be the hardest-working brass band in Providence. The 20-piece outfit plays souped-up Balkan funk and has a new album out on punk label Don Giovanni Records.

School Of HONK

Saturday set times: 2 p.m. at the corner of Elm and Grove; 5 p.m. at 7 Hills Park

Honk bands are, for the most part, amateur affairs, open to participants of all skill levels. School of HONK, a Somerville-based nonprofit, takes that inclusive spirit to the next level. Every Sunday the organization hosts a free community jam session and parade in which anyone, regardless of experience, is invited to pick up an instrument and join in. If you’re interested honk-style brass band music, School of HONK is a great place to start. Plus, it puts on a pretty good show.