Several fisheries are over-exploited and may collapse; yet the amounts of fish processing by-products containing muscle proteins and ω-3-rich oil are staggering. The by-products are land-filled, ground and discarded or otherwise diverted from human consumption. Due to the lack of technology to recover proteins and lipids from by-products or low-value species, this tremendous resource is unavailable for human consumption. Isoelectric solubilisation/precipitation (ISP) allows efficient recovery of fish proteins and oil which retain functionality and nutritional value of food products. Isoelectric point (pI) is a pH where protein maintains zero electrostatic charge. At pI, protein–protein hydrophobic attraction overcomes protein–water electrostatic attraction resulting in isoelectric precipitation. Conversely, isoelectric solubilisation occurs at a pH different from pI, whereby protein–water attraction and protein–protein electrostatic repulsion are favoured. Therefore, protein solubility/insolubility is induced by ISP, respectively. Consequently, ISP allows selective protein recovery. Lipids are also recovered during ISP processing. This article reviews recent ISP developments to recover proteins and lipids from by-products and low-value marine species.