Nature has bestowed Pakistan with plentiful resources including algae, which are being utilised for the extraction of metals, phycocolloids, oil, cholesterol free protein and fertilisers. Algae have attracted pharmaceutical and synthesis industries for their commercial exploitation. These organisms include essential fatty acids (EFAs) such as linoleic, arachidonic, linolenic, ?-linolenic acids etc. that must be in diet for healthy growth. These acids cannot be synthesized fast enough by body to meet needs. Present research work aimed at isolation and characterisation of saturated and unsaturated fatty acids from seaweeds and freshwater algae collected from the Karachi coast of northern Arabian Sea as well as various areas of the Sindh Province, Pakistan. This book exhibits comparison of fatty acid composition between various algal phyla, different classes and orders as well as the inhabitants of marine, brackish water and freshwater environments. Such an extensive account of fatty acids with updated references will not only be valuable for a wide range of enthusiastic researchers but also inspire prosperous industrialists to extract economically important fatty acids at large scale.