A session (seisiún in Irish) is an informal gathering of musicians who play tunes usually in a pub. In "open" sessions anyone is free to join in (provided they know the tunes). It's also one of the best ways to hear this music.  To find a session near you, check out thesession.org (it's also a great resource for tunes!)

Open Sessions in NYC  

Monday

Click on the venue for more info
Landmark Tavern
626 11th Ave at 46th St.  A lively session in an historical landmark tavern, led by Don Meade.
(212) 247-2562Monday 8-11PM

Iona Scottish Session
180 Grand Street, Brooklyn. Is Scottish music your thing? Then this is the session for you.
Mondays 9PM-late

Tuesday

Dempsey’s Session at Sláinte
304 Bowery (between Houston and Bleeker). Led by John Nevin and friends. Open to musicians of all levels. This is the session I call home.  I'm here every Tuesday. 
Tuesday 8–11PM

The Green Room 
156 E. 23rd Street (btw Lexington & 3rd Aves). A bi-weekly open seisiún.
Every other Tuesday 8-11

Wednesday

The Kensington Seisiún / Shenanigan's Pub (Brooklyn)
Shenanigan's Pub, 802 Caton Avenue,  Brooklyn, NY.  Ann Murphy Leads this session.
Wednesday 8PM

Dunne's Pub 
15 Shapham Place, White Plains, NY.  914-421-1451. Fiddle master Brian Conway leads this session in White Plains.  
Wednesday 7PM

Thursday

Mary O's
32 Avenue A (between 2nd & 3rd).  Open to musicians of all levels, but aimed at the learning musician. Lots of fiddlers! Led by Caitlin Warbelow and friends.  I love this session.  You'll find me here on a Thursday night. 
Thursday 8-10PM; after session (leaderless) 10:15PM -11:30PM

Fitzgerald's 1928 Pub
13 Herman Street, Glen Ridge, NJ. A nice session in a pub with great food. Steve Wickens and guests. Near the train station.  Thursday 8-11PM

Saturday

Slow Session at NYIC
1040 Jackson Ave, LIC (7 train).  Know only a few tunes? Go here. Friendly and welcoming, and not in pub with observers. Saturdays 1:30-4 PM

Sunday

Craobh Úll Mór CCÉ Seisiún
1040 Jackson Ave, LIC. A friendly open session. The 3rd Sunday of every month 4-7PM

The Hutton
225 Hutton St., Jersey City, NJ 07307.  A friendly open session at a lovely gastropub in Jersey City.  3PM -5:30.

For the most complete line up of traditional music sessions, concerts and festivals, check out Ceol Agus Rince.