From the CATalyst Council:
"Approximately 4 million cats end up in shelters every year, including thousands born every spring and summer during “kitten season.” To help promote adoptions of these fun, affectionate animals, American Humane celebrates Adopt-A-Cat Month each June.
"Your local shelter is brimming with cats of every breed, age and personality just waiting for a loving home. Whether you prefer young and frisky or mature and mellow, you’re sure to find the perfect cat companion during Adopt-A-Cat Month!"
Over at their website they have some excellent educational materials:
CATegorical Care: An Owner's Guide to America's #1 Pet (PDF)
Connecting With Cats (PDF), a children's coloring book
About the American Humane Association (PDF)
Feline resources from the AVMA
Adopt-A-Cat Month recognized in Congress