Abstract: Systems and methods for delivering implantable devices, catheters, or substances in or near and/or restoring flow through body lumens, such as blood vessel lumens are described. A catheter having a proximal portion of a first diameter and a distal portion of a second diameter (smaller than the first diameter) is advanced into a body lumen. The distal portion of the catheter is caused to expand to a diameter that is larger than the second diameter but no larger than the first diameter. A working device is then advanced out of the distal end of the catheter and used to remove obstructive matter, deliver an implantable device or substance and/or restore flow. The distal portion can be reduced in diameter prior to removal from the body. A stand alone, guide catheter is also disclosed possessing high resistance to kinking even with a very thin wall.