Fluorine, be it as individual atoms or CF3 groups, facilitates and orients the deprotonation of arenes and hetarenes (pyridines etc.). Representative examples will illustrate the concept of "optional site selectivity" in organometallic reactions. Using fluorine as a mechanistic probe, further details of the Wittig reaction sequence have been elucidated. Improved protocols for cis- and trans-selective olefination processes will be disclosed. Organofluorine chemists are often confronted with one central issue:. "What is the effective size of the smallest halogen". A new approach to answer this intriguing question is based on the comparison of organoleptic properties. [on SciFinder (R)]