This chapter enters with the theoretical concepts, which are then applied in chapter 4 to practice, in order to explain the existence and role outsourcing of the procurement as well as to formulate recommendations for action for the organization of an efficient procurement process.
The first represented concept is the transaction cost theory, which represents the main beginning of the theoretical view of this work and in chapter 3.1 is described. Chapter 3.2 presents Activity based the Costing beginning, which is suitable for a cost analysis of the enterprise-internal procurement process in particular.
After the transition from the transaction cost theory to the ABC beginning in chapter 3.3 one describes, chapter 3.4 finally combines the concepts mentioned, in order to come into a uniform theoretical analysis model.

The transaction cost theory belongs to the "new Institutional Economics" paradigm and regards accordingly the enterprise as organization form ⁹ .
This opinion decreases/goes back to the thesis of Coase, those the market and the company as institutional arrangements describes ¹⁰ .
The transaction cost theory is to contribute to the decision of the most suitable organization form decision, whereby the best alternative is identified mainly on basis of the cost comparison ¹¹ .
This implies an analysis of different forms of economical organization regarding the transactions and their dimensions, which can be completed and organized in them. Before one enters more in greater detail however with the straight connections mentioned, an explanation of the central terms and acceptance is necessary.

⁹ Vgl. Rindfleisch/Haide (1997), P. 31.
¹⁰ Vgl. Coase (1937).
¹¹ Vgl. Williamson (1991), P. 269.

The investigation core is the transaction, which is to be understood as exchange of a property or a service between transaction partners. There each transaction a contractual agreement - market, hierarchical or hybrid - subordinated, the transaction partners are simultaneous contracting party ¹³ .
The transaction costs represent the costs of the completion and organization of the economic exchange between transaction partners and them imply both ex ante and ex post office-transaction-cost ¹⁴ . "ex ante transaction costs cover the costs of the achievements, which lead to the conclusion of a contractual agreement, in particular thus information -, costs of the contract and negotiation.
Ex post office-transaction-cost contain the costs, which develop for the security, penetration and possible adjustment of the contractual agreements.
" ¹⁵ belongs beyond that to the transaction costs also the opportunity costs, those from inefficient organization decisions originates in ^{to 16} .
The transaction costs, i.e. costs, which develop for the contracting parties for the completion and organization of the transaction, but also production costs, i.e. costs, which develop for the contracting parties for the production of the exchanged goods or achievements, are not only yardstick of the advantage of an institutional arrangement.
With the comparison of the efficiency more alternatively institutional arrangements accordingly the sum of production costs and the transaction costs resulting in each case are taken as a basis ¹⁷ .
In addition it is not easy to quantify and cause-fairly add those for the production of a property which can be exchanged or an achievement as well as for the preparation and completion of a transaction resulting costs.
The transaction cost theory is interested however not in the exact absolute height of these costs, but wants to only determine, in which institutional arrangement for a certain transaction higher and into which lower costs to result.
After Simon often impudent and simple arguments are sufficient to determine around a difference between two sizes ¹⁹ . For the understanding of the transaction cost theory an explanation not only their concepts, but also its acceptance is important. Three behavior acceptance are the basis this theory:

• Limited rationality: The participants tend to act rationally in the result succeed to them however only imperfectly this. This both due to the limited information is caused, which they have, and due to their limited data processing and communication capacity.
• Opportunismus: The transaction partners pursue their own interest with the organization of the exchange relationship. It is counted on the possibility that it here also cunning, deception, restraint of information etc. to begin.
• Risk neutrality: Neutral risk inclination of the participants.