【正文】 ive binations. Network configurations also shape the outes of both alliances and their partnering organizations. As an organizational field evolves and institutionalizes, it develops stable positions, identified by clusters of firms that exhibit specially dense collaborative ties to one another, but sparser or nonexistent alliances with other organizational positions. Our objective is to investigate dynamic structural changes in the strategic alliance networks of the global information sector (GIS) from 1989 to 2000, a period when this organizational field experience major transformations in technology and economic petition. This multiindustry sector enpasses the 145 largest North American, European, and Asian firms that either manufacture equipment (semiconductors。 puters。 peripheral devices) or create, distribute, and provide access to diverse informational content (satellite, wire, cellular, and pager telemunications。 software and database publishing。 newspaper and magazine publishing。 motion pictures, video and sound recording。 radio, television, and cablecasting). Analyzing data on 3,571 strategic alliance announcements, we examine changes occurring at both macro and microlevels over the twelve years. Time trends reveal that accelerating rates of alliance formation resulted in increasing numbers of new alliances across the twelve years, with mean organizational centralization peaking in the mid1990s. Among the 30 mostactive firms, structural differentiation increased across three years spanning the 1990s, with smaller, more specialized clusters emerging. By 2000, the Japanese panies had substantially concentrated their new alliance agreements among themselves, contradicting the globalization hypothesis that information organizations would create a stable alliance network structure consisting of a core block occupied by corporations from different nations. Our dynamic models of network evolution across the three years revealed that the 30 core panies chose alliance partners that increased two structural properties. Organizations sought new connections with organizations that had direct and indirect ties resembling their own alliance propensities. At the macrolevel, these changing ties among the core global information sector firms generated a more differentiated strategic alliance network, one exhibiting greater structural balance and extensively circuitous linkages that enlarged the collective opportunity to forge new partnerships. Most studies of alliance formation processes focus on microlevel dyadic relations, that is, on a pair of organizations creating a new partnership. In general, strategic alliance formation consists of these three sequentially linked decision processes: identification of goals that an organization want to achieve by entering into a strategic alliance, identification of a suitable partner, and choice of governance forms for the prospective alliance. Empirical analysts have made fruitful contributions to understanding these processes, including decisions to collaborate。 selection of alliance partners。 and choice of governance form. Institutional and resource dependence theories explain why organizations engage in network relations with others. Institutional theorists argued that organizations try to enhance their legitimacy in a field through interorganizational relationships . One study of nonprofit foundations discovered that cooperation with other service providers is a frequently stipulated condition for social service agencies to receive large study of nonprofit foundations discovered that cooperation with other service providers is a frequently stipulated condition for social service agencies to receive large grants. Resource dependence theorists asserted that organizations enter strategic alliance to gain critical resources such as money, information, technology, and market. At the same time, organizations in the alliance also avoid overdependence on their partners that would risk their general, organizational core location within networks, prior ties to prospective partners, and middle managers’ personal connections all affect the search for a suitable partner and the governance forms used to manage the alliance. The search for strategic partners and governance forms can be a frustrating process for many organizations that lack network leverage from previously wellestablish relations with other firms in the field. Researchers have examined a broad range of alliance consequences such as alliance management, acplishment of alliance and partner goals, and organizational performance indicators such as innovation rates, product proliferation, and market petition or collusion. Larson investigated four alliances among seven establishments operating in a diverse set of industries. She found that trust and reciprocity replaced administrative hierarchy and arm’s length market to govern alliance partners in their daily exchanges. Organizations rarely relied on written contracts, administrative controls, economic incentives, or market data to coordinate their transactions with partners. Instead, to maintain a stable and sustained relationship, organizations constantly use informal and implicit contracts, which derived from prior ties, interpersonal relations, and reputation knowledge. Larson’s research also indicated that organizations must mit resources to understand and adapt to their partners’ needs. For interorganizational ties to continue, organizational willingness and capacity to devote resources to tailor their partners’ interests must consistently be present. In an analysis of semiconductor firms from 19851991, Stuart investigated the impact of alliances on firm innovation rates and economic growth, measured respectively as the number of patents granted and growth as annual semiconductor sales. The crucial factors were not the size of each firm’s alliance portfolio, but the resource profiles of its partners. Specifically, both innovat