The adoption of 3D printing into mainstream manufacturing is considered not only as a highly flexible processing technique, but also as a technique that can be applied to functional materials such as inks, paste, polymers, ceramics, powders and organic materials. Advanced processing techniques such as extrusion-based printing and ink-based printing technologies are at the forefront of 3D printing technology. In traditional manufacturing, the ability to select from a variety of preformed processable polymers is a challenge. 3D printing, however, predominantly targets the production of polymeric parts and models, and gas sensors are no exception. Advantages of conducting polymers such as good sensitivity, selectivity, synthetic richness, low-temperature operation, low cost of materials, and the inkjet deposition of polymer material allow integration of sensor arrays and supporting circuitry. As a result, the designed sensor is capable of multi-parameter sensing such as mobility, transconductance, threshold voltage, thermochromism, electrochromism, gasochromism, etc. This review focuses on a recent breakthrough in 3D printed sensors for detecting pressure, temperature, gas, electric fields and color when exposed to external stimuli. It also discusses sensors which are 3D printed and/or integrated within 3D printed structures, particularly, polymer-based gas sensors and gasochromic devices.