Selectrix is a digital model train command control system developed by German company Döhler & Haas for model railway manufacturer Trix in early 1980s. Originally the system was proprietary and commercialized exclusively by Trix. In 1999 the two companies mutually agreed to terminate their exclusive licensing agreement and since then, Selectrix has become a widely recognized standard and is supported by several equipment manufacturers in Europe. European Model Train Association, MOROP has covered Selectrix partially in their NEM standards.

Selectrix is technically more advanced than its main competitor, widely accepted Digital Command Control (DCC) system. Selectrix has bus speeds much faster than those in DCC and the size of the locomotive decoders is diminutive in comparison to decoders of other systems. The smallest Selectrix decoder is less than 2 mm thick and therefore ideal for the smallest model railway scales like Z scale and N scale.

Computer chips for the System come exclusively from Döhler & Haas. Several manufacturers offer Selectrix products based on D&H chips. The most important manufacturers are Trix, Rautenhaus and Müt-Digirail. Unlike in DCC-technology, Selectrix components from various manufacturers are compatible at all levels and can be freely combined in real-world Selectrix control solutions.