Which countries make up Western Europe?
I imagine that this answer depends on several factors.
If you are asking in a socioeconomic way, then you probably are only considering a Western Europe and Eastern Europe. In this case, the map might be split in half, with the usually-accepted border being the language family border - Slavic-language countries (and Hungary) are usually considered Eastern Europe, and Germanic and Latin languages are Western Europe, though there are exceptions (e.g., Romania).
The United Nations has a "Western Europe and Others" group, where Western Europe includes: Andorra, Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Liechtenstein, Luxembourg, Malta, Monaco, Netherlands, Norway, Portugal, San Marino, Spain, Sweden, Switzerland, and the United Kingdom.
If you split Europe up more geographically, as a news article might, there could be a Western Europe, Eastern Europe, Central Europe, Southern Europe, and Northern Europe.
Here, Western Europe would include: Portugal, Andorra, Spain, France, Germany, Netherlands, Belgium, Luxembourg, Switzerland, etc. Some might throw in Italy and Denmark or perhaps remove some others.
Some might include a subset called Southwestern Europe, including Spain, Portugal, and Andorra.
Tough question! :)