Despite anecdotal evidence of changes to tennis ball characteristics and play properties, little research has been directed towards understanding the causes and effects of tennis ball degradation. Improved racket technology and player fitness have contributed to an increase in the speed of the game, yet balls have seen few advancements over the same period. There are several obvious factors contributing to tennis ball degradation: natural pressure loss in pressurised balls, changes to the cloth covering due to court and racket impacts, and precipitation and environmental factors. As recent tennis research has focused on the new balls, there is a need to investigate other ball conditions present in the game of tennis. This thesis provides a structured investigation into the causes and effects of ball degradation, an objective assessment of the effects of degradation on ball performance, and incorporates subjective perceptions of all aesthetics and play properties noted by players. Particular attention is given to ball fuzziness. Excessive fuzziness can occur from manufacturing variability, court and racket interactions, and environmental conditions - though there is currently no standardised method to assess ball surface condition. An objective measure of ball fuzziness has been developed and used in the analysis of nearly 4000 individual ball images. The effects of court and racket impacts, precipitation, natural pressure loss, and repeated impacts have been analysed for their effects on ball degradation. An assessment of ball performance utilised ball impact and aerodynamic data to determine significant differences between balls and develop an improved ball trajectory model.