Due To Resource Limitations As Well As Vulnerability To Physical Capture Of Sensor Nodes, Traditional Public Key Security Protocols (E.G., RSA, Diffie-Hellman Key Exchange, Elliptic Curve Cryptography (ECC), Elgamal Cryptosystem, Etc.) Are Too Complicated And Energy-Consuming For Largescale Wireless Sensor Networks. As A Result, Symmetric Ciphers Such As DES, IDEA, RC5, AES Are The Viable Options For Encryption/Decryption Of Secret Data. In Order To Establish Symmetric Secret Keys Between Communicating Sensor Nodes In A Sensor Network, We Typically Use The Bootstrapping Protocol. This Protocol Establishes Cryptographically Secure Communication Links Among The Communicating Sensor Nodes. However, This Is A Challenging Area Of Research Due To Resource Limitations And Physical Insecurity Of Sensor Nodes. Since Wireless Sensor Networks Are Often Operated In An Unattended Mode, An Adversary May Physically Capture Some Sensors To Compromise Their Stored Sensitive Data As Well As Communication Secret Keys. Therefore, Any Adversary That Gets Hold Of A Sensor Node Can Easily Extract Its Stored Cryptographic Information. These Features And Challenges Motivate The Research On Development Of Secure Key Distribution Mechanisms For Wireless Sensor Networks. In This Thesis, Secure Key Distribution Mechanisms Are Studied. The First Study Is Based On Improvements Of The Path Key Establishment Phase Of The Bootstrapping Protocol In Static Wireless Sensor Networks. We Have Developed Two Location-Adaptive Key Establishment Schemes, Namely, The Key Forwarding Scheme And The Multi-Hop Key Forwarding Scheme Which Achieve Significantly Better Network Performances As Well As Security Against Node Capture As Compared To Those For The Path Key Establishment. The Second Study Is Devoted On The Identity-Based Random Key Distribution Mechanism In Static Wireless Sensor Networks. We Have Proposed A Technique To Achieve This Goal. The Proposed Technique Provides Better Network Performances And Security Against Node Capture As Compared To Those For The Existing Schemes. The Third Study Investigates How To Improve Performances Of The Existing Location-Aware Key Distribution Schemes In Static Wireless Sensor Networks. We Have Designed The Location-Aware T-