As of November 2009, KLM  Economy Class passengers may bring only 1 piece of check-in baggage free of charge on flights between Europe and the United States or Canada.  Special fee: Economy Class passengers can check in a second piece of luggage at a flat fee of EUR 50. When departing the United States, this fee is USD 50, or CAD 50 when leaving Canada. The fee for a second piece applies only to tickets purchased after November 1st. Flying Blue Elite members
As a Flying Blue Silver, Gold or Platinum member, you can bring 2 pieces of check-in luggage free of cost. Neither are you charged for the second piece if you travel in World Business Class.
Check in online and get a discount

A second piece can easily be paid for when checking in. If you arrange for this piece when checking in online via KLM.com, you pay 20% less: all you need is a credit card. Then hand over your luggage at a baggage drop-off point at the airport. Of course you can also arrange for your excess baggage at the check-in desk at the airport.
Piece concept

Our flights between Europe (including Algeria, Morocco and Tunisia), and the United States or Canada fall under the piece concept. This means that on these routes, you may bring a number of pieces of check-in luggage. Your free baggage allowance is always stated on your e-ticket. And of course you can find all details on baggage on our website.

Read more about your check-in luggage
Read more about travel to the United States
View the list of flights under the piece concept