Preheat oven to 350°F (175°C). In large mixer bowl, cream butter and sugar until light and fluffy. Add eggs and vanilla; beat well. Sift together flour, cocoa, baking soda, and salt; gradually blend into creamed mixture. Stir in chocolate chips. Drop by spoonfuls onto ungreased cookie sheets. Bake 8 to 9 minutes. DO NOT over bake! Cookies will be soft. Cool slightly on cookie sheet; transfer from sheet onto wire rack to cool completely.
1 1/4 cups butter or margarine, softened - 2 cups granulated sugar - 2 large eggs - 2 teaspoons vanilla extract - 2 cups all-purpose flour - 3/4 cup unsweetened baking cocoa - 1 teaspoon baking soda - 1/2 teaspoon salt - 2 cups chocolate chips.