This chapter is devoted to a brief presentation of the Diamond Model, an integrative model that is supposed to guide and simplify the whole diagnostic and therapeutic work. This model has the following traits: (a) It is multi-systemic. Every case is a product of a dynamic interaction between programs belonging to many subsystems within the person and outside the person. The subsystems can be looked at synchronically or diachronically. Each of the internal programs develops along fixed parameters. (b) The Diamond Model is a synthesis of concepts and methods drawn from multiple sources. (c) It is linguistically uniform. The whole diagnostic and therapeutic discourse can be formulated in the same explicit theoretical languages – semiotics, information processing and cybernetics. (d) The etiology of each case is explained by the same principle of simplicity. Programs can lose their simplicity in periods of drastic change and crisis, in which the persons' emotions get off-balance. They become infected with bugs – horse blinders (lack of comprehensiveness), fifth-wheel (lack of parsimony), flip-flop (lack of consistency) and non-sense (lack of plausibility). A typical dysfunctional strategy used in such situations is restoring simplicity partially. The bugs prevent the programs from enlisting homeostasis-maintaining corrective feedback. The result is dysfunctional feed-forward, escalating deviation from the desired homeostasis. Therapy in general and play therapy in particular should aim at removing or weakening the bugs, by restoring the balance of bugs-maintaining emotions that got off-balance and by activating various "bug-busters" or "play bug-busters". Therapy should also aim at restoring the programs’ capacity for learning and development. (e) The choice or creation of bug-busters, emotion-balancing techniques and techniques promoting learning and development is subject to the principle of technical eclecticism. Any technique from any source can be employed if it can serve the above-mentioned purposes.