  Blazars are the most numerous type of observed high-energy gamma-ray
emitters. However, their emission mechanisms and population properties are
still not well-understood. Crucial to this understanding are their cosmological
redshifts, which are often not easy to obtain. This presents a great challenge
to the next-generation ground-based observatory for very-high-energy gamma
rays, the Cherenkov Telescope Array (CTA), which aims to detect a large number
of distant blazars to study their intrinsic emission properties and to place
tight constraints on the extragalactic background light density, amongst
others. The successful investigation of these subjects needs a precise redshift
determination. Motivated by these challenges, the CTA redshift task force
initiated more than 3 years ago a spectroscopic observing program using some of
the largest optical and infrared telescopes to measure the redshifts of a large
fraction of blazars that are likely to be detected with CTA. In this
proceedings, we give an overview of the CTA redshift task force, discuss some
of the difficulties associated with measuring the redshifts of blazars and
present our sample selection and observing strategies. We end the proceedings
with reporting selected results from the program, the on-going collaborative
efforts and our plans for the future.
