Bio aerosols can be detected and classified at stand-off ranges using lidar techniques. Elastic lidar refers to the lidar technique where molecules and aerosols are detected by their elastic backscatter. This report analyzes elastic lidar for detecting of a remote bio aerosol cloud. The authors are analyzing and reviewing some elastic lidar concepts with respect to the choice of laser wavelength, receiver subsystem, detection techniques and estimates the system performance under various atmospheric conditions. The report identifies the wavelength of 1.5 µm as appropriate with respect to good performance and laser source availability. Signal processing methods are reviewed and a lidar waveform simulation tool has been developed. Minimum detectable concentrations of bio aerosols are estimated and processing techniques for detection of weak cloud returns are discussed. The analysis is supported by some limited amount of experimental lidar data. Complementing techniques like UV laser induced bio fluorescence are needed for the verification process determining whether the cloud is a Bio aerosol and whether this might be dangerous or not. These techniques are treated elsewhere. This work is a result of a pre-study on a stand-off lidar demonstrator for Bio aerosol detection now being under development at FOI.