Should you purchase theater tickets before departing for London? The answer is yes . . . and no. If you want to see a specific performance of a specific play, then buy tickets in advance -- especially if that show is at the Royal National Theatre, the Donmar, the Globe or the Almeida. Because of their enormous popularity, short runs and limited capacity, tickets for those venues sell out fast. If you don't know your schedule, prefer flexibility or want to take your chances at the half-price tkts booth (see below), then wait until you're there.

Whether buying in the United States or London, first call the theater's box office or check its Web site. Booking fees (Britspeak for service charges) vary; most are in the $4 to $10 range, although some go as high as 25 percent of face value. Some theaters waive the booking fee if you call the box office directly. Given the vagaries of U.S. mail, opt to pick up the tickets at the theater rather than having them mailed.

Other sources for tickets include:

* Ticket agencies, although their Fringe theater offerings are limited. Try Keith Prowse (800-669-8687, www.keithprowse.com) or Ticketmaster (011-44-161-385-3500, www.ticketmaster.co.uk).

* Hotel concierges have a knack for getting tickets -- but often at a considerable markup, plus tip.

* Tkts, the city's only official discount theater ticket booth, in Leicester Square. Half-price and discount tickets are available for performances that day, with a handling fee of about $4.50 per ticket. Most of the tickets are for West End musicals and long-running comedies, but tickets to Off-West End shows sometimes turn up here. The booth is open Monday through Saturday 10 a.m. to 7 p.m., Sunday noon to 3 (ish). A good strategy is to arrive just before it opens, study the bulletin board that lists what's on offer, then get in line. You can pay with cash, credit card or debit card; personal checks and travelers checks are not accepted. To find out what's available, go to www.officiallondontheatre.co.uk/tkts. The list is updated daily at noon, London time.

-- Susan Davidson