This book is designed to have a comprehensive review of the spectrum of diseases involving orbital apex and periorbital skull base and the up-to-date advancement in different treatment modalities. Management of diseases at the orbital apex and periorbital skull base has always been a challenge. Multiple specialties are involved, including skull base neurosurgeon, oculoplastic ophthalmologist, otorhinolaryngologist, head and neck surgeon, oncologist, neurologist and radiologist. However, frequently it results into a “no-man’s land”, as no single specialty is entirely familiar with this complex and overlapping anatomical territory. Cranial nerves, carotid artery, and cavernous sinus are just one of the few examples of important anatomical structures that pass through. However, this has often been managed by one specialty especially during surgical planning and operation, resulting in biases in choices of approach and surgical strategies. We believe that this interesting yet complex region deserves special attention with a well-orchestrated multi-disciplinary effort. Traditionally, surgical treatments for diseases in this region involve different types of craniotomy and orbitotomy.  In this book, it covers the advancement in imaging modalities, medical therapies, operative instruments, radiation therapy namely stereotactic radiosurgery or radiotherapy, management of diseases in orbital apex and periorbital skull base evolve and improve with time.  Minimally invasive surgery in terms of mastering neuro-endoscopy contributes to the intervention advancement.