Molecules of Murder is about infamous murderers and famous victims; about people like Harold Shipman, Adelaide Bartlett, and Georgi Markov. The talk will analyse the crimes from the viewpoint of the poison itself, and by so doing throw a new light on how the murders or attempted murders were carried out and ultimately how the perpetrators were uncovered and brought to justice. The first half of the talk is about natural toxins which were originally used by doctors before becoming notorious as murder weapons. The second half of the talk deals mainly with man-made molecules and how they too have been dangerously misused in famous crimes. The talk ends with the most famous unsolved poisoning case in recent years, that of Alexander Litvinenko who was murdered with polonium chloride. Our knowledge of this poison points an accusing finger at his assassin.