PMI offers 2 kinds of Project Management certifications for Management professionals. First and foremost highly accredited PMP certification and stepping stone certification CAPM. PMI offers Certifications in other categories in Program management (PgPM) and OPM3, the maturity model certifications. I'll cover Program Management in other section but I'll focus Project Management topics in this current section. I definitely recommend Stanford Advanced Project Management course at http://apm.stanford.edu/, which is the best place on earth to learn Program management and Portfolio management.
Let us talk about PMP certification over here. Why do you need it? This certification is globally acknowledged and respected credential. Globally is appropriate word but in UK Prince 2 certification enjoys wider acceptance. Lets compare PMP and Prince 2. Prince 2 is a framework and the PMP which is based on PMBOK is collection of Knowledge Areas and both are difference breads. A framework provides templates and repeatable processes. PMBOK the guide for PMP doesn't provide such templates. Most important, if you are in a job market this certification definitely makes the difference. Even if the employer doesn't follow PMBOK principles as a PMP you can always have better perspective of Projects.
Getting PMP certification is not a simple process. But with an exam strategy it would not be that impossible. You also need to have certain educational standards and Project Management experience. A major misconception is that Project Management experience means people think that they need to be Project Manager all along. But Project contributor experience is also valid for the certification. PMI doesn't look for Manager title, but the real Project contribution experience is sufficient. That means a Senior Developer or Business analyst who contributed to projects are eligible for PMP certification.