Water vapor is known as the key atmospheric coupling element of almost all microscopic (e.g. formation of drop-lets/ice crystals), macroscopic (e.g. clouds/precipitation) and global processes (hydrological cycle). However, particularly for airborne hygrometers, significant systematic (±10%) and dynamic (±30%) discrepancies still remain even between established and intensively used instruments. One possible reason for this is their lack of a connection to the international metrological humidity scale. This humidity scale serves as an accurate reference for the establishment of comparability between different instruments. Typically, depending on the humidity range, the metrological uncertainty of this scale is about 0.3% (k = 2) or better. The aim of this thesis, therefore, was to develop a new class of field-qualified, metrologically validated laser hygrometers which have a direct linkage to the international humidity scale, but also avoid the usual, error-prone instrument calibration. In addition, the hygrometers should provide the most important features needed for airborne monitoring, too. This includes, inter alia, a very high dynamic range (3–40000 ppmv H2O), high measurement speed (>1 Hz), and high precision (< 0.2 ppmv) in combination with high reliability and robustness. This thesis describes the development, construction and validation of in total five different, completely new Tunable Diode Laser Absorption Spectroscopy (TDLAS) hygrometers: one TDLAS hygrometer developed for laboratory feasibility studies and four compact, autonomous, and aircraft-approved laser hygrometers. The airborne spectrometers include two spectrometers at λ = 1.4 µm (SEALDH-I and SEALDH-II) with solely extractive sampling, a complex multi-phase, multi-channel hygrometer (HAI-Ia) simultaneously working at λ = 1.4 & 2.6 µm, and its further upgrade (HAI-Ib) for the most recent HALO mission. The need for a miniaturized, robust spectrometer has led to broad range of special developments e.g., highly accurate and robust spectral laser stabilization along with the holistic treatment of parasitic absorptions in free-space- as well as fiber-coupled spectrometers. Two of these innovative assemblies were filed for patent. In addition to extensive validation procedures under well-controlled laboratory and simulated (in terms of temperature, vibration, ambient humidity) flight conditions at traceable metrological H2O standards, the first side-by-side comparison and validation of a calibration-free TDLAS hygrometer with a national primary H2O standard was realized. This validation confirmed the metrologically calculated total uncertainty of 4.3% ±3 ppmv over the entire "p, T, c" range of the hygrometer. In more extensive measurement series, the long-term stability was determined over 18 months to be μ = 0.2% and σ = 0.3%. Owing to the complex stabilization and the holistic monitoring of the instrument, the unwanted temperature influence on the instrument response function – one of the most important perturbations in field situations – could be minimized to a relative H2O concentration error of only 0.02%/K. Thus, for the first time calibration-free, airborne TDLAS H2O measurements could be successfully demonstrated on various research aircrafts over the entire water vapor concentration range in the troposphere and lower stratosphere. During six flight campaigns (in total 250 net flight hours) 100% data capture and maximum reliability were achieved. This also allowed the first in-flight comparisons of the extractive (closed-path) hygrometer with many established H2O instruments (e.g. CR2, WVSS-II, FISH) and (in collaboration with Forschungszentrum Jülich) the first sampling-free gas phase measurement with an open-path White cell mounted directly on the outer fuselage of the HALO research aircraft. In addition, via the multi-phase hygrometer HAI, direct synchronous multi-phase H2O measurements in ice-, liquid-, and mixed-phase clouds could be realized for the first time with a single instrument for simultaneous open- and closed-path H2O measurements. The HAI multi-channel hygrometer also allowed the first successful cross-validation of the open-path detection with the metrologically validated closed-path spectrometer under clear-sky conditions. HAI’s open-path cell could also be employed for the first calibration-free high-speed optical pressure sensing on a research aircraft. This optical pressure sensor was compared to a micromechanical pressure sensor (deviations < 1%, depending on range). The pressure measurements showed the first evidence of strong (up to 30%) aircraft-orientation-induced local pressure offsets on the fuselage. The high precision of HAI (closed-path: lab ~19 ppbv at 100 ppmv - 10 Hz, in-flight ~67 ppbv at 10 ppmv - 10 Hz, open-path: in flight ~13000 ppbv at 900 km/h - 6000 ppmv - 10 Hz), the high time resolution (Δt = 1.35 ms at 120 Hz data rate) and the proven resolution capabilities for strong and rapid H2O gradients (up to 26 000 ppmv/s) of the closed-path cells allowed the investigation of very fine spatial H2O structures (Δl = 35 cm at v = 900 km/h) – especially in clouds. SEALDH-II and HAI (closed-path) participated in the international hygrometer comparison campaign (AquaVIT-II) and showed deviations in the low percentage range (e.g. 100–1000 ppmv H2O: average deviation ~2% 20–350 ppmv, av. ~1.3%). The overall campaign data of all hygrometers are still being investigated at KIT. In summary, these new hygrometers enable for the first time a close connection between meteorology and metrology. In the future, they will provide the atmospheric community with powerful tools for the calibration-free, accurate, fast and reliable quantification of atmospheric water contents over the entire troposphere up to the lower stratosphere. Through their linkage to the metrological humidity scale, the instruments may contribute to a significant improvement in the accuracy and comparability of water measurements and serve as field-proven gold standards for atmospheric monitoring networks.