In some last years mid-infrared EnYAG laser radiation (2940 nm) found the exploitation in many applications in technology and especially in various medical branches (dentistry, dermatology, cardiology, ophthalmology). Most of them use the EnYAG laser system working in free-running regime generating the pulses with the length of some hundreds of microseconds. In the presented work we concentrated on the development and optimization of electro-optically Q-switched EnYAG laser and suitable delivery system. Er:YAG laser operated both in free-running or Q-switched regime was developed and optimized. LiNbO 3 Pockels cell was utilized for Q-switching the Er:YAG laser. Single giant pulses with maximal energy 67 mJ and minimal duration 53 ns FWHM were generated for maximal pump energy 131 J and for the optimal Pockels cell parameters (high voltage value 1.4 kV, delay of Pockels cell switching after the flashlamp trigger 450 μs). The Er:YAG laser radiation was effectively delivered by the special COP/Ag hollow glass waveguides with inner/outer diameters 700/850 μm or 320/450 μm, and length from 10 cm up to 1 m. The transmission of the used waveguides was measured to be from 73% to 84% according to waveguide type. With the help of delivery systems, the EnYAG laser radiation (in the form of long pulses for free-running regime or short pulses for Q-switched regime) was applied to various biological tissue samples to study the basic laser radiation - tissue interactions and treatment possibilities.