This thesis investigates the potential for improving the control of the microclimate within agricultural buildings, by experimenting with the application of proven and advanced control algorithms used in other fields. The Proportional-Integral-Plus (PIP) control system design methodology has been applied to two micro-environmental chambers. The PEP control design has been extended with a number of procedures that linearize a normally non-linear system. These procedures may be applied at either the design stage or implemented as extra elements to the actual controller. Taking the process a stage further, a full adaptive PIP control design has been implemented on the Leuven chamber. Additionally, a unique fan/valve controller was designed and implemented on the (Leuven) ventilation chamber with considerable success. The primary aim of this research has been to further develop an automatic forced ventilation control system suitable for imperfectly mixed air spaces within agricultural buildings. The final contribution of this research has been the Lancaster micro-environmental chamber. This was designed, built and instrumented in Lancaster. Previously no similar facility existed at Lancaster and the chamber is now an integrated high quality adaptable research test chamber for carrying out a vast array of experimental work in modelling and control with the capacity to test theories in a real scale building structure. The facility has also been used as a teaching aid for control courses in both Engineering and Environmental Science at Lancaster, and will continue to be used for teaching.