The West Island is the western part of the island of Montreal. It is mainly a residential suburb of the city of Montreal. It is the location of Montreal Pierre Elliott Trudeau Airport and McGill University's Macdonald Campus. The residents are mostly English speakers (or "anglophones"), in contrast to the mostly French speaking residents of the rest of Montreal. (Currently, about 42% of the population is anglophone, 31% is French-speaking or "francophone", and 25% is "other.")
Despite the name, the "West Island" isn't actually its own island. It is an informal name for the western tip of the island of Montreal. Two other islands (Île-Bizard and Île-Perrot), just off the western tip of Montreal, are often considered part of the West Island. The Montreal suburbs of Lachine and Lasalle are usually not considered part of the West Island, although they are also mainly residential and anglophone.
The West Island encompasses the following suburbs of Montreal (some are boroughs of the city of Montreal; others are separate municipalities):
Montreal's airport, Pierre Elliott Trudeau Airport (formerly Dorval Airport) is in the West Island. To get from the airport to other locales in the West Island, you can do the following:
From Ottawa, Highway 417 eastbound becomes Autoroute 40 at the Ontario/Quebec border. Keep following Autoroute 40 until you cross the Ile-aux-Tourtes bridge (a 90-minute drive).
From Toronto, Highway 401 eastbound becomes Autoroute 20 at the Ontario/Quebec border. Keep following Autoroute 20 until you cross the Galipeault bridge (a 5 hour drive).
From Quebec City, Autoroutes 20 and 40 westbound both arrive in the West Island. Follow the signs to Montreal; once there, follow the signs to Toronto/Ottawa.
From Boston or New York, take the usual route to Montreal; For instance, from NY, the I-87 through the Adirondacks, across the Bernard-de-Lacolle/Champlain border crossing; this becomes the 15 north, which takes you to the Champlain bridge. Once you cross the bridge onto the Island of Montreal, follow the signs to Ottawa/Toronto via the 20 or 40 Westbound highways.
VIA Rail's trains from Ottawa and Toronto stop at the VIA Rail station in Dorval on the West Island. From there, you can walk or take a shuttle bus to the commuter train/bus station.
Montreal's Agence Metropolitaine de Transport(AMT) operates two commuter train lines to the West Island. The "Deux-Montagnes" line leaves from Gare Centrale and stops at Sunnybrooke and Roxboro-Pierrefonds. The "Vaudreuil-Hudson" line leaves from Gare Lucien-L'Allier and Vendôme stations and stops in in Lachine, Dorval, Pointe-Claire, Beaconsfield, Baie-d'Urfé, and Sainte-Anne-de-Bellevue. These trains are relatively infrequent, so it is advisable to check the schedule on the website of the AMT. 
Busses from Ottawa and Toronto to Montreal stop on Avenue Saint-Charles, Kirkland, on the West Island.
Montreal's STM operates city busses to most parts of the West Island. These are usually numbered with three digits beginning with "2" (such as 201, 203, 204). Routes from Montreal usually begin at metro stations. For more details on bus routes, consult the website of the STM or look at the large public transport maps found in all of Montreal's metro stations and most bus shelters. 
Because the large geography, extensive highway system, and paltry public transport of the West Island, a car is by far the most convenient way to get around the West Island. Autoroute 40 covers the northern part of the West Island, taking you to Pierrefonds, Dollard-des-Ormeaux, Fairview Shopping Centre, and Senneville. Autoroute 20 covers the south, taking you to Dorval (including the Airport), Kirkland, Pointe-Claire, Baie-d'Urfé, and Sainte-Anne-de-Bellevue (including the Macdonald Campus).
The two autoroutes, which go east-west, are connected via the following north-south roads in the West Island: Avenue des Anciens Combattants, Avenue St-Charles, Boulevard Saint-Jean, Avenue des Sources, Autoroute 13, and Autoroute Côte-de-Liesse. Getting from one highway to the other takes 5 min without traffic but up to 20 min at rush hour.
People without cars take the bus to get around the West Island. $3.25 one way, transfers included (exact change required). Fairview Pointe-Claire shopping mall, at the corner of Autoroute 40 and Avenue St-Jean, is the hub for most bus services. Other bus connection points include Dorval commuter bus station (at the intersection of Autoroute 20 and Côte-de-Liesse) and McGill's Macdonald Campus in Sainte-Anne-de-Bellevue.
Lakeshore Road, along the shore of the St. Lawrence River, is an enjoyable ride by bicycle (although the narrow road is shared by cars). The West Island does not offer many bicycle paths. Be alert, however, as cyclists on major roads are relatively rare, so drivers do not always look out for them. Remember that snow and ice can be a very real obstacle for cyclists from the end of November through to the beginning of April.
The West Island is mostly a collection of residential suburbs and there isn't much in the way of tourist attractions. That said, there are a few places of interest if you find yourself stuck out there.
Pointe-Claire Village is a quaint collection of shops and restaurants in Pointe-Claire, near the waterfront. Farther west, Sainte-Anne-de-Bellevue Village has more quaint waterfront spots, including some very good restaurants at prices far lower than what you'd pay downtown. This can make for an escape from hustle and bustle on a nice summer night.
Fairview Pointe-Claire shopping mall houses some generally high end fashion stores and boutiques. Due to its location and relative busy neighborhood, it is generally considered to be the center of the West Island. Other places to shop include Dorval Shopping Centre ("Les Jardins de Dorval"), "Les Galeries des Sources" in Dollard-des-Ormeaux, and the outlet retail shops near Colisée Kirkland. The shopping in the West Island is utilitarian and functional, but not particularly interesting; all the necessities are accessible, but the experience is somewhat generic.
Montreal's three best-known specialties are available on the West Island.
An entire range of restaurants, from fast food chains to expensive sit-downs, are to be found on Rue Saint-Jean in Pointe-Claire and Boulevard des Sources in Dollard-des-Ormeaux. Most restaurants are family-style and many of them tend to go out of business quickly.
More difficult to access, but generally better, restaurants with nice views are to be found on Lakeshore Road, along the edge of the St. Lawrence River. Several "villages" (i.e. historic districts) are located along this road, where bakeries, sit-down restaurants, and the occasional bar are concentrated. Pointe-Claire Village and Sainte-Anne-de-Bellevue Village are two examples of this. Also, a few more midrange/upscale restaurants have opened in other areas of the West Island in recent years, responding to the population shifts in the area. An example is Autoroute 40 West (TransCanadoam at Boulevard des Sources), which offers downtown-style fine dining in a West Island location.
The West Island is predominantly suburban and residential, so the nightlife and drinking culture is subdued compared to Montreal.
Ste-Anne-de-Bellevue Street in Ste-Anne-de-Bellevue (aka "Saint Anne's"), with its proximity to McGill's Macdonald Campus and John Abbott College, is the closest thing to a lively drinking area in the West Island with a limited number of bars. The Macdonald Campus also hosts a student-run bar on Wednesdays and Thursdays.
A small number of cafes and bars can be found in the other main commercial areas of the West Island (such as Boulevard Saint-Jean, Boulevard des Sources, Pointe-Claire Village). A couple of new places have opened up, notably a McKibbin's Irish Pub in Pointe-Claire. There's also the old standby of Bourbon Street West on Boulevard des Sources, which has live music quite often and attracts a bit of an older crowd.
West Island nightspots tend to be more crowded in the wintertime, when going all the way downtown feels like too much of a hassle to go for just a beer. Like those in Montreal, West Island bars serve predominantly Quebec and Canadian beers from producers such as Molson, Labatt, and Unibroue, with a limited selection of American and other imported beers.
Hotels and Inns are close to Fairview Pointe-Claire shopping mall and Pierre Elliott Trudeau Airport. The hotels in Dorval and along Côte-de-Liesse tend to be more generic airport hotels, such as Sheraton Four Points, Holiday Inn, Travelodge, EconoTravel, etc. Since the West Island is mostly suburban and residential, there aren'tmany options beyond that. Boutique hotels, hostels, and places with character can be found mostly in the more touristy downtown area. Never underestimate the appeal of sleeping on the sofa of a friend, however. The price is right!
With downtown Montreal only a short commute to the east, it is the destination of choice for most people wanting to get out of the West Island. If one has access to a car, there are also some other interesting, albeit quiet, destinations to the west of the West Island: