A PhD will provide you advancement in your career, usually a hefty salary differential, and prestige. You should thoroughly research career prospects before you commit to a program: some fields, such as the humanities, are increasingly glutted with PhDs, making it near impossible to land a job at all, especially if you are seeking a job as a professor. Other fields are expanding. Logically, if a field is growing in its need for research, and is connected with powerful policy decision-making, then a PhD in that field will be an asset. PhDs in economics, finance, marketing, and development studies, just to name a few, are solid bets for future job and salary prospects.