A fundamental concept of science is to recognize, understand, and utilize functional principles of nature. Immunoassay development is a good example of this as it borrows the specific recognition of target compounds by antibodies as a key functional element from nature. The combination of the different functional elements “target recognition” and “signal generation/signal amplification” is now the core of all immunoassay applications. By introducing the polymerase chain reaction (PCR) as a tool for exponential signal amplification in immunoassays, a range of advanced applications with increased sensitivity became accessible. The “immuno-PCR” assay thereby reveals an exceptionally broad dynamic detection range. With now over 30 years of laboratory use, immuno-PCR has established itself as a versatile, flexible, robust, and ultra-sensitive assay platform technology, especially for analysis from small sample volumes (microsampling) and/or multiple targets from a single sample (polyplex).