We discuss some selected attempts to describe collective consequences of social
interactions in terms of a phase transition. Attention is paid to the structure
of social networks. The case of the hierarchical network [1,2] is considered
as a recent example. This network is a mathematical realization of the concept
of weak ties [3]. Consequences of the scale-free noise in a social environment are also
discussed [4].

[1] D. J. Watts, P. S. Dodds and M. E. J. Newman, Science 296 (2002) 1303.
[2] M. Wołoszyn, D. Stauffer and K. Kułakowski, Eur. Phys. J. B. 57 (2007) 331.
[3] M. Granovetter, Sociological Theory 1 (1983) 201.
[4] D. Stauffer and K. Kułakowski, arXiv:0709.3811