Who does a government shutdown affect most? Here's what happens to the agencies Americans rely on.

With an Oct. 1 deadline to fund the government looming and no deal in Congress in sight, the prospect of a government shutdown has many Americans wondering what the impact of a lapse in government funding might mean for the services they depend on.

A shutdown occurs when Congress fails to approve new spending for federal agencies, which are generally barred from spending money without congressional authorization. There are some exceptions, like activities needed to protect life and property. Each agency makes its own determination about which employees are needed to stay...