For established companies, I've always had a written employment agreement which discussed some terms common to all employees, including anti-moonlighting, usually ip assignment, etc. But I don't think I've ever had a contract that described what I going to do... maybe when I worked for a school district, but there my position title didn't actually match the work anyway; the position title was about being a tech helper in the classroom, but my position was at the district office with field work that only rarely had interaction with students.