Echoing several responses above, the PM has many important responsibilities. However, I believe that these responsibilities would not be as challenging as communicating effectively amongst all department/ functional areas working together on the project. There needs to be a great deal of transparency which can only be achieved through clear timely communication in order to hold project team members engaged and accountable for current goals, issues, progress, and deadlines. The PM has many tools to accomplish the communication whether it be through e-mail, phone call, meetings, etc. however how he/she relays the message is very important in promoting an environment for collaboration and teamwork. The effective communication would be one critical challenge PM faces that can put a project on a success direction or not.