The focus in this article is on the biophysics and morphogenesis of large algal cells, defined here as having a volume (including cell wall and all intracellular compartments) of ≥1 mm3. After surveying the taxonomic distribution of giant algal cells as individual organisms and as parts of multinucleate organisms, the nuclear DNA content of the giant cells and its distribution between one or (more commonly) many nuclei is considered. Among the biophysical aspects of nuclear function in large cells, and especially uninucleate cells, are the large distance (0.5 mm or more) that products of transcription and/or translation have to travel within uninucleate algal cells, and the means by which intracellular differentiation to produce ‘roots’, ‘stolons’ and ‘leaves’ can occur in multinucleate (coenocytic) (and to a lesser extent uninucleate) algal cells. A key role for the cytoskeleton seems likely, but there are still problems of defining the location of the products of gene expression and hence the morphogenetic effects. The analysis of the vegetative functioning of the organisms produced by this cellular morphogenesis shows little influence on resource (light, nutrients) acquisition of the absence of division into many small cells within a defined overall morphology and size.