Advanced Squad Leader (ASL) is probably the most popular board wargame in the world.  Its subject is tactical combat in the World War II era.  ASL is not a single stand-alone game, but rather a modular game system whose components collectively allow you to experience tactical combat in any theater of World War II. 

The extent and variety of ASL is truly astounding; if you can imagine a type of fighting in World War II, ASL can represent it.  Fighting in the rubble of Stalingrad?  Check.  Storming the beaches of Normandy?  Check.  Staving off Rommel at Tobruk?  Check.  Clearing Japanese from caves in Okinawa?  Check.  Finnish ski troops?  Polish cavalry?  Yugoslav partisans?  Filipino conscripts?  Japanese paratroopers?   Belgian snipers?  Check. 

Virtually every weapon and vehicle that appeared in World War II also make an appearance in ASL.  German King Tiger tanks.  Sherman amphibious tanks.  Japanese "knee" mortars.  Recoilless rifles.  Bulgarian panzers.  "Wasp" flamethrowing vehicles.  Molotov cocktail projectors.  Stukas.  Naval artillery.  Even the dreaded "Sturmtiger." 

To represent all of these exciting things, ASL needs a lot of rules and, sure enough, it comes with a thick rulebook.  But the genius of ASL is that it is actually easy to learn, because the core systems that govern movement and conflict are not complicated and can be learned in minutes (indeed, the ASL Starter Kits, which eliminate most of the chrome to concentrate on the core rules, allow people to be up and running in minutes).  Most of the rules are rules for specific circumstances.  If you are not playing a scenario set in the desert, you can completely ignore the desert rules.  This also allows people to learn at their own pace.

Gameplay in ASL is centered on the "scenario."  A scenario is a representation of a specific tactical action.  Do you remember the episode in "Band of Brothers" depicting Easy Company's assault on the German artillery battery position at Brecourt during the Normandy invasion?  That might be an ASL scenario.  ASL scenarios vary considerably in size and nature, but a "typical" ASL scenario might depict an action in which a player controls the actions of 100-300 soldiers, perhaps accompanied by 1-8 vehicles and/or guns.  ASL scenarios provide historical context and information, specify which maps and counters to use, provide special rules to simulate that specific situation, and provide "victory conditions" for each side.  Depending on its size, a scenario might take from a couple of hours to a full day to play.  Most scenarios probably take around four or five hours to play (including set-up time).

What makes ASL so highly addictive as a game is that it is incredibly interactive and incredibly immersive.  It "sucks you in" to the game in a way that virtually no boardgame ever does.  Many people have described the experience of playing an ASL scenario as like making their own World War II movie—that is how visual it is and how strong a narrative flow ASL scenarios have.  If you play an ASL scenario, you experience a "story."  Moreover, there is no "down time" in ASL.  The game is so interactive that there is no waiting for your opponent to make his moves.  Both players are constantly confronted with decisions to make, decisions that could significantly affect the outcome of the scenario.  The result is that ASL is amazingly mentally stimulating.  Your brain is overclocked when you play ASL, it is racing as fast as it can.  When you play ASL, you immerse yourself in a complete gaming experience.  You will want to come back again and again.

And when you play ASL, you have a world of options open to you.  First, there are literally thousands of different scenarios published.  You can reach for your favorite "classic" scenarios to enjoy them again, but you can also always—always!—have fresh new scenarios to play as well.  There is so much variety that you could play a different scenario every single day for well over a decade and still not play them all. 

However, in addition to scenarios, there are other ways to play ASL.  Two in particular are worth mentioning.  The first is the so-called "Historical ASL Module" or HASL.  HASLs are major products devoted to a specific military action with detailed historical maps and rules for that conflict.  Some past HASLs have included the fighting for the Red Barricades factory complex at Stalingrad, the Marine Corps invasion of Tarawa in 1943, and the fight for the "bridge too far" at Arnhem in 1944.  HASLs offer not only the thrill of playing on detailed historical maps, but also something called a "campaign game," which offers an extended playing experience.  ASL campaign games offer a unique strategic element by depicting tactical level fighting over an extended period of time—days or even weeks.  Through multiple playing sessions, players must be masters of strategy as well as tactics, assembling their forces, creating plans, and conducting extended attacks, defenses and counterattacks.  The fondest memories for many ASLers are from their first campaign game experience.  Many campaign games are also large enough to allow for the possibility of team play, which can be tremendously fun.

Another way to play ASL is through solitaire play.  While individual ASL scenarios may be able to be played solitaire, there is a whole game subsystem, Solitaire ASL (SASL) which provides rules and counters for players to undertake a variety of solitaire missions.  The game system provides rules for the governance of the "enemy" force.  Although one of the real thrills of ASL is its face to face play, SASL offers a very different playing experience that many ASLers enjoy quite a bit.

ASL is called Advanced Squad Leader because it is descended from a (long out of print) 1977 game called Squad Leader, designed by John Hill and published by Avalon Hill.  This game, the first tactical squad level game ever, was a best-seller and tremendously popular.  It introduced many of the concepts that still govern ASL.  Over the next seven years, three additional "gamettes" were published adding additional components, complexity and chrome.  By the early 1980s, it was getting pretty confusing.  There were several different rulebooks to go through, several different iterations of counter design, and other problems.  Expanding the system further threatened to put too much strain on it.

What Avalon Hill decided to do instead was to re-do Squad Leader, combining, revising and refining all the rules of the original system, as well as adding new systems to make it more universal.  The new rules would be accompanied by a modular system of components that could be purchased piece by piece.  The result was Advanced Squad Leader, appearing in 1986.  It too was an immediate hit and quickly developed a dedicated following.  Indeed, the demand for ASL material was so great that Avalon Hill could not satisfy demand, with the result that many people and companies (the so called "third party" publishers) began publishing "unofficial" ASL materials. 

Eventually, ASL outlived Avalon Hill itself.  The venerable wargame publishers had long been facing financial hard times.  In 1998, their parent company decided to sell its gaming assets to toy giant Hasbro and concentrate instead on other ventures.  But a small company, Multi-Man Publishing (MMP), which began as a "third party" publisher, then signed on as the designers and developers of Avalon Hill's ASL line, reached a licensing agreement with Hasbro that would allow it to keep the ASL line alive.  For the past 10 years, ASL has been the flagship of MMP's line of board wargames.  They have been good stewards of one of the best strategy games ever created.