You're accountable for getting a project done, and you need assistance and cooperation from a number of people. There is a gap, however, between your responsibility and your authority level. Maybe you aren't high enough on the totem pole to tell people what to do, or maybe even if you are, command and control is just not your style. No matter how high up the corporate ladder you are, you will find yourself interacting with groups of people that you need to influence without pulling rank.
People forget that leadership is, first and foremost, a service.
If you are not a person that fulfills a need for the people you lead, then you have no business being a leader, regardless of your rank in the company. The service you provide might be providing information, representing people and projects to outside parties or higher-ups, engaging people to cooperate, imparting a sense of accomplishment and a sense of security. In short, your job is to help THEM be successful, even more than it is their job to help you succeed. You must be known as a person who works hard on behalf of the group, knows his stuff, does his homework, plays fair, and honestly provides information and admits mistakes. Having these qualities won't instantly make you a leader, but NOT having these qualities will instantly take you out of the running.