The tendentious decrease in global arable land and the fast increment in world population will inevitably lead to a critical point. It is therefore imperative to protect crops from pathogen attack. Their deleterious impact on human health is not better, with several invasive infections reaching mortality rates up to 80%. The door is definitely open for biological control, based on molecular interactions between host and pathogen. The remarkable coding capacity of oligosaccharides, far superior to those of nucleotides and amino acids, justifies the emergence of the sugar code as the third life code. The word exoglycome is proposed to represent the oligosaccharide side chains presented at the outer surface of cell membranes, thus excluding the cell wall carbohydrates. The exoglycome plays a fundamental role in cell-cell recognition, in distinction between self from non-self, in the warfare between host and pathogen before infection is established, and in certain diseases such as cancer. Unlike pathogen cell wall carbohydrates, the exoglycome has been neglected as a target for developing effective ways to control disease. Pathogens often induce changes in their cell wall and/or exoglycome to elude and/or circumvent host defences. Identification of such host-induced alterations may prove extremely important for both treatment and diagnosis. Reading the sugar-encoded messages is mainly played by a class of carbohydrate-binding receptors called lectins. The available evidence strongly suggests that a large number of lectins remain to be discovered. Their role in defence should not be underestimated. A high-throughput procedure capable of single-step isolation of novel lections from previously unknown biological samples has recently been developed.