The basics:
The city's celebration is older than the constitution, dating back to the Dutch days of 1766. Still strictly marchers-only (no cars or floats allowed), this year's 245th annual parade is officially dedicated to the Fighting 69th Infantry of the New York Army National Guard who served in Iraq and the 19 who were killed in action. The festivities begin with a blessing from Cardinal Edward M. Egan, Archbishop of New York, who will celebrate mass at St. Patrick's Cathedral at 8:30 a.m.—not long before crowds start gathering along the parade route.
• Friday, March 17, 11 a.m. to approximately 5:30 p.m.
• The parade begins at 44th St. and Fifth Ave. and proceeds north along Fifth Ave. to 86th St.
• Free

The best vantage points:
• Any spot along Fifth Avenue toward the north end of the parade route, far from midtown's shopping and work crowds and the NBC camera crews.
• The steps of the Metropolitan Museum of Art (1000 Fifth Ave. at 82nd St.) are a particularly good bet since marchers often pause outside the nearby American Irish Historical Society.
• The official reviewing stand lies at 64th Street, and free tickets are available for bleachers running from 62nd to 65th streets. Seating is on a first-come first-served basis and many more tickets are distributed than seats are available. Call 718-793-1600.

The participants:
• Cardinal Edward M. Egan officially reviews the parade and greets crowds from the steps of St. Patrick's Cathedral.
• Mayor Bloomberg marches along with a crop of local politicians: Speaker of the City Council Gifford Miller and the borough presidents.
• Grand Marshall Timothy J. Rooney, son of Arthur Rooney, the founder of the Pittsburgh Steelers, and associate member of the New York and American Stock Exchanges, leads the parade.
• The famed 69th Regiment marches at the head of the parade as the Grand Marshall's military escort.
• Royal Canadian Mounty Police march behind the NYPD.
• FDNY Commissioner Hayden Scoppetti marches with other FDNY members.
• Bagpipe bands from Birmingham, England; Spain's Gallaica region; counties Tipperary and Carlow, Ireland; and elsewhere.
• High school bands from across the country.
• Irish societies and interest groups from the U.S.A. and the motherland: Youghel, and counties Cork and Carlow, Ireland.

The television coverage:
• Armchair spectators can tune in to NBC, channel 4, which will be taping live from 11 a.m. to 3 p.m. at various points along the parade route.