The star ranking system in Europe rates hotels, in general, from 0 to 5 stars.  So, can you reliably select a hotel and be sure that a 3 star hotel is better than a 2 star hotel or that a 4 star hotel is better than a 3 star, for instance.  Well, it's not as easy as that.

How are stars assigned?  Again, in general, stars are assigned to the amenities and quality of service offered by a hotel.  For instance, does it have a restaurant?  Does it provide parking?  Does it have A/C? Are there concierge services?  In some areas, it would be important to know if a private bathroom is in every room.

One thing you can almost be 100% sure of, the higher the star rating of a hotel, the higher the price.

But in general:

• No stars – You probably don’t want to stay here.
• 1 Star – Probably no private bath.  No A/C.  Other than the hotels mentioned below, you probably don’t want to stay here either.
• 2 Star – The better ones have private baths and are clean and comfortable.  An interior decorator has probably never seen the inside of these hotels.  Good ones have hair dryers, elevators, but maybe not A/C.   Hotels in this class are usually smaller properties.
• 3 Star – Sometimes small and charming, but some can have well over a hundred rooms.  Private bath.    Most have A/C.  Usually a safe bet.
• 4 Star – Quality, full service hotels.  Still, rooms may be smaller than what is found in the U.S. 
• 4 Star luxe and 5 Star –   Some of the best luxury hotels in the world.

What is not greatly considered in giving a hotel a star rating is the location of the hotel.  So, you could select a highly rated hotel and be located far from where you might want to be. Also given little consideration is the size of a room.   I have stayed at a 5-star Paris hotel in a smaller room than many 2 star hotels I have stayed at.

How to get a bargain:  If traveling to Europe in the winter, get a hotel with no A/C, restaurant, or parking.  It might have a lower star rating because it does not have these amenities you would not use anyway, and therefore, a lower price.

By the way, The Traveling Professor's blog posts have plenty of recommended hotels for your next European stay.