ontal layers (customer, service or network management). Established companies are likely to prefer strategies close to the network management layer at the bottom, whereas new entrants more likely appear close to the customer interface on the top. On the one hand, this is due to the similarity of CRM processes across industries and, on the other, due to required domain expertise on network technologies that cannot be transferred from other vertical software markets. Broad strategy. A vendor possessing broad expertise on both telecom specific technologies and processes. Such a vendor provides OSS products for several segments, at least one of the vertical segments and/or one of the horizontal layers as described above and in Fig. 1. The market scope strategy used by the vendors has yet another dimension: the extent of vendor's focus on telecommunications. This is related to the evolution of software industry, where software production generally shifts gradually from Overview of Telecom Operator Software Market in-house production, first to external producers, and then further to general, i.e., horizontal software firms (see Section "Shift of Software Development Activity" in Chapter "Model for Evolution of a Vertical Software Industry"). Vendors with a telecommunications industry focus can be divided into three categories: (1) telecommunications-specific vendor with more than 90% of revenue from the telecommunications industry; (2) telecommunications industry dependent vendor with more than half (50-90%) of its revenue from the telecommunications industry; and (3) horizontal software vendor with a majority of revenue from the outside of the telecommunications industry (i.e., <50% of revenue from the telecommuni- cations industry). Together, the breadth of a firm's operations and the extent of focus on the telecommunications industry can be used in order to classify the OSS/BSS vendor strategies: the breadth of a firm's operations can be used as one dimension for measuring an OSS vendors' market strategy, while the 