Laboratory-based experimentation is an increasingly popular method for conducting network research since it enables implementations of network systems and protocols to be evaluated. Most research conducted in lab-based environments requires the faithful reproduction of wide area network conditions. An important step toward satisfying this requirement is the creation of paths between nodes in the lab that have the same characteristics as paths between nodes in the Internet. In this paper, we describe and evaluate a new, highly scalable, software-based path emulation tool called NetPath. We describe the design and implementation of NetPath, which features fixed and probabilistic packet propagation delay emulation, probabilistic bit errors, probabilistic packet loss, packet duplication, and packet reordering capability. Through a series of controlled laboratory experiments, we demonstrate that Net- Path offers over three times the loss-free throughput capacity of other popular software-based path/network emulators. We show that under moderate load NetPath?s mean propagation delay emulation precision is within 1% of a hardware-based reference emulator. This result represents a significant improvement over other software-based emulators. We illustrate how, relative to our hardware-based reference, NetPath improves application traffic behavior over other software-based emulators. Finally, we demonstrate and characterize NetPath?s ability to provide path emulation simultaneously on multiple physical links. This capability, which is facilitated through the use of our link configuration tool, enables laboratory system resources to be more efficiently utilized.