There are many libraries to work with many different types of biometric. Depends of what type of biometric you will work.
Most common is fingerprint. If you want a free library you can try NBIS from NIST. Therefore if you want a better library you can try Aware or Neurotechnology libraries. And you can talk with vendor of your biometric sensor asking a library. Many biometric devices vendors have free libraries to customer that buy they devices, like Suprema, Crossmatch, Nitgen, Fujitsu, SRI,...
Please elaborate better your question telling us what biometric type you want to work: fingerprint, facial, finger vein, palm vein, DNA, signature, keystrokes, etc...