Since highly proliferative carcinomas with a neuroendocrine phenotype but poor histological differentiation grade are extremely rare in the jejuno-ileum, management of such cases remains highly individual and can currently not be considered standardised according to organ-oriented guidelines. For the management of such cases, the reader is referred to previous guidelines [4]. This chapter, therefore, deals with non-metastatic NEN originating from the small bowel and the appendix as originally described as ‘carcinoid’tumours by Oberndorfer [5] in 1907. For greater ease of use, jejuno-ileal NEN (part 1), appendiceal NEN (part 2) and GCC (part 3) are discussed in separate sections.