Filamentous organisms are important industrially used microorganisms due to their exceptional production and secretion capacities. The morphology of filamentous organisms in submerged cultivations is of special importance mainly because of the impact on process productivity. The understanding of complex interconnections between morphology and bioreactor conditions is basic for a successful bioprocess design. From the engineering point of view the effect of morphological form on broth rheology is the most important aspect. Morphology of filamentous fungi which is developing in any fermentation system can be considered as a final result of various influences, an equilibrium between forces of cohesion and disintegration. It is well known that a specific growth form is required for optimal production of certain metabolites (especially secondary). The forms that are occurring can differ from freely dispersed mycelium to interwined clumps and dense spherical pellets. Cultivation parameters such as type and concentration of inoculum, media composition, pH value, temperature, agitation, aeration and novel methods of filamentous growth engineering by addition of microparticles in cultivation broth were studied in this work. In addition, the methods for characterization of morphology in fermentation systems and rheological models to evaluate the state of fermentation broths are summarized.