The viability of the systems depends on the way of adaptation of the internal complexity to the environmental complexity. Under structural aspect, any complex system represents a network. Complexity may be estimated on the basis of density and of the non-redundant character of the network. The capacity of the networks to create and diffuse knowledge is essential. Comparing the change speed of the environment with the knowledge processing speed in the system, we can determine the maximum complexity that can be absorbed. A close image of the internal complexity is the level of the human and structural capital. The external complexity may be expressed by means of the relational capital.