Mostly, he taught me about friendship and selflessness and, above all else, unwavering loyalty.

When I wrote 'Marley & Me,' I had a clear audience in mind. And it did not include children. I wrote my book for adults and assumed only adults, and possibly teenagers, would be drawn to it.

In a dog's life, some plaster would fall, some cushions would open, some rugs would shred. Like any relationship, this one had its costs. They were costs we came to accept and balance against the joy and amusement and protection and companionship he gave us.

A dog doesn't care if you're rich or poor, educated or illiterate, clever or dull. Give him your heart and he will give you his.

It's just the most amazing thing to love a dog, isn't it? It makes our relationships with people seem as boring as a bowl of oatmeal.

A dog has no use for fancy cars or big homes or designer clothes. Status symbols mean nothing to him. A waterlogged stick will do just fine. A dog judges others not by their color or creed or class but by who they are inside. A dog doesn't care if you're rich or poor, educated or illiterate, clever or dull. Give him your heart and he will give you his.

A person can learn a lot from a dog, even a loopy one like ours. Marley taught me about living each day with unbridled exuberance and joy, about seizing the moment and following your heart. He taught me to appreciate the simple things-a walk in the woods, a fresh snowfall, a nap in a shaft of winter sunlight. And as he grew old and achy, he taught me about optimism in the face of adversity. Mostly, he taught me about friendship and selflessness and, above all else, unwavering loyalty.