Spiro compounds (also named as spiranes following the suggestion of Adolf von Baeyer as early as 1900) are ubiquitous molecules, which contain a fused bicyclic system that share a single atom. A search for the key term “spiro” in the SciFinder database at the beginning of April 2017 resulted in more than 147,000 hits including 5000–6000 publications per annum after 2010. This enormous research activity encompasses a large number of fields in chemistry (especially organic and medicinal chemistry—with an emphasis on heterocyclic systems), but also includes pharmacology, crystallography, materials science, physics, biochemistry, molecular biology, engineering, energy and fuels, just to mention the most active areas. The immense interest in spirocycles, besides their unique features related to isolation from natural sources, synthesis and stereochemistry, is fuelled by an extremely wide range of useful properties, that comprise among others anti-cancer, antibacterial, antifungal, anti-diabetic, anti-HIV, cytotoxic, diuretic, spasmolytic, antiphlogistic, anti-hypertensive, anti-depressant, anxiolytic, anti-fouling, anti-feedant, herbicidal, plant growth regulatory effects; photochromism; and hole-transporting ability.