Superelastic and/or shape memory nickel-titanium alloys having an increased fatigue life that is superior to known nickel-titanium alloys are disclosed. The nickel-titanium alloys have a minimum fatigue life that may be at least about 10 million strain cycles at a strain of at least about 0.75. The minimum fatigue life may be due, at least in part, to the nickel-titanium alloy having at least one of an oxygen concentration of less than about 200 ppm, a carbon concentration of less than about 200 ppm, the absence of oxide-based and/or carbide-based inclusions having a size greater than about 5 microns (μm), the presence of an R-phase, or combinations of the foregoing. Articles manufactured from such fatigue-resistant nickel-titanium alloys can be more durable because they are more resistant to repetitive strain and crack propagation.