When G-d placed Adam in the Garden of Eden, He told him both to subdue the earth (Genesis 1:28) but also to protect it (2:15). We see that man is allowed to use the works of creation but not to abuse them. So, while we may eat meat and use leather or fur, we may not cause needless pain or harm to animals.
But what about such things as animal testing of cosmetics? Does that constitute use or abuse? Rabbi Dr. Asher Meir, better known as “The Jewish Ethicist,” examines this question in a three-part series, beginning here.