Cooperative behavior among unrelated individuals in human and animal societies represents a most intriguing puzzle to scientists in various disciplines. Here we present a simple yet effective mechanism promoting cooperation under full anonymity by allowing for voluntary participation in public goods games. This natural extension leads to rock-scissors-paper type cyclic dominance of the three strategies cooperate, defect and loner i.e. those unwilling to participate in the public enterprise. In spatial settings with players arranged on a regular lattice this results in interesting dynamical properties and intriguing spatio-temporal patterns. In particular, variations of the value of the public good leads to transitions between one-, two-and three-strategy states which are either in the class of directed percolation or show interesting analogies to Ising-type models. Although volunteering is incapable of stabilizing cooperation, it efficiently prevents successful spreading of selfish behavior and enables cooperators to persist at substantial levels. PACS numbers: 05.50.+q, 87.23.Cc In behavioral sciences and more recently in economics the evolution of cooperation among unrelated individuals represents one of the most stunning phenomena [1,2]. The prisoner's dilemma (PD) has long established as a paradigm to explain cooperative behavior through pairwise interactions [3]. While the PD attracted attention from biologists and social scientists, most studies in experimental economics focused on the closely related but more general public goods game (PGG) for group interactions [4]. In typical PGG experiments, an experimenter endows e.g. four players with $ 10 each. The players then have the opportunity to invest part or all of their money into a common pool. They know that the total amount in the pool is doubled and equally divided among all participants irrespective of their contributions. If everybody cooperates and contributes their money, each player ends up with $ 20. However, every player faces the temptation to defect and to free-ride on the other player's contributions by withholding the money since every invested dollar returns only 50 cents to the investor. Obviously, defection represents the dominating strategy leading to the 'rational' equilibrium where no one increases its initial capital. Such strategical behavior prescribed to homo oeconomicus is frequently at odds with experimental findings [5] and lead to the decline of this rationality concept.Note that for pairwise encounters with a fixed investment amount, the PGG reduces to the PD. PGG interactions are abundant in animal and human societies [6,7,8]. Consider for example predator inspection behavior, alarm calls and group defense as well as health insurance, public transportation or environmental issues, to name only a few.Recently it was demonstrated that voluntary participation in such public enterprises may provide an escape hatch out of economic stalemate and results in a substantial and persistent * Present address:Department of Zoology, Uni...