This paper introduces a class of entanglement measures that satisfy certain conditions and shows that the Quantum Relative Entropy and Bures Metric generate two such measures. The authors calculate the entanglement of mixed two-spin-1/2 systems using the Quantum Relative Entropy and provide an efficient numerical method for this calculation. They also prove several properties of their entanglement measure, which have important physical implications. The paper discusses the statistical basis of their measure in the case of the Quantum Relative Entropy and relates their measure to purification procedures. They argue that their entanglement measure determines an upper bound on the number of singlets that can be obtained by any purification procedure. The paper also presents a number of examples and proves several properties of their measure. The authors show that the entanglement of creation is generally larger than the entanglement of distillation. The paper concludes with a discussion of the physical meaning of their measure and its relation to purification procedures.This paper introduces a class of entanglement measures that satisfy certain conditions and shows that the Quantum Relative Entropy and Bures Metric generate two such measures. The authors calculate the entanglement of mixed two-spin-1/2 systems using the Quantum Relative Entropy and provide an efficient numerical method for this calculation. They also prove several properties of their entanglement measure, which have important physical implications. The paper discusses the statistical basis of their measure in the case of the Quantum Relative Entropy and relates their measure to purification procedures. They argue that their entanglement measure determines an upper bound on the number of singlets that can be obtained by any purification procedure. The paper also presents a number of examples and proves several properties of their measure. The authors show that the entanglement of creation is generally larger than the entanglement of distillation. The paper concludes with a discussion of the physical meaning of their measure and its relation to purification procedures.