Why Do Piano Keys Stick?

There are 1000 different reasons why piano keys stick but most commonly is a change in humidity or temperature.  As you change the environment around the piano it will have to acclimate which can effect the keys.

Typically when you start running your A/C or Heat for the season or after you move a piano, the keys can stick for a short time.  If your keys are sticking longer then a week, there's a different problem that needs to be addressed.