The paper deals with creating the terminology of the theory of conceptual integration by applying the basic terminology principles. This theory is a new branch of cognitive linguistics, having been developing from the 1990s with its roots in the theory of conceptual metaphor which began developing in the 1980s, and Fauconnier's theory of mental spaces. Since the theory of conceptual integration has been developing for the last thirty-or-so years, and the fundamental book The Way We Think by Mark Turner and Gilles Fauconnier still has not been translated to Croatian, and although the literature in English is extensive, there can be found only a couple of papers, parts of the paper or shorter articles in Croatian about the theory mentioned above. In those couples (i. e. ten) of papers, inconsistencies are noticeable, so one could conclude that the terminology of the theory of conceptual integration does not exist in Croatian terminology, or if it does, it is in disarray. When reading about the theory of conceptual integration in Croatian literature, only few and mostly used or common English terms of the theory of conceptual integration can be found formed in Croatian, but most of them are used in their original forms in English. Although a small number of these English terms is formed and defined in Croatian, when considering quantity, most of the English terms are mentioned in English, not Croatian, and also without being defined or not mentioned at all. With that being said, when reading and studying the theory of conceptual integration, researchers have to read the literature in the English language, which is not a problem in itself. The problem emerges when a researcher decides to write a paper about the theory of conceptual integration in, for example, Croatian language. Three options are possible – one, one can write and use terms in the English language, second, one can write and use the most common and used terms formed in Croatian, and the rest of the terms in English, and third, before writing a paper, one can create, organize, and systematize the terminology of the theory of conceptual integration in Croatian, which is a challenging task. Each field's terminology is a part of standard Croatian language which means that the creation of any terminology should not be formed randomly, inconsistently, or partially. The standardization in the Croatian language includes creating the terminology of the field, in this example the terminology of the theory of conceptual integration, following basic terminology principles, and defining the terms following basic defining principles. In the Croatian terminology, nine basic principles of forming the field’s one can be found, and the previously mentioned terminology principles are applied when creating the terminology of the theory of conceptual integration with the goal of systematized, standardized, and established terminology. Moreover, when creating the single term and terminology in general in Croatian language, the aim is to apply all nine terminology principles and two possibilities occurred. Firstly, when creating and forming the term in Croatian, all principles were considered and applied, and secondly, one terminology principle interfered with another. If one principle was interfering with the other, a hierarchy of principles was assessed and established to take as many principles as possible into account and to combine them. Also, it was taken into consideration that although metaphor affects unambiguous and effective scientific communication, and scientific language avoids it, the metalanguage of the theory of conceptual integration deals with the creations of secondary meanings and novel metaphors, which is metaphoric in itself. The methodology of the work is based on the application of basic terminological principles to the creation of the terminology of the theory of conceptual integration. Terminological principles are taken into consideration in three different situations: 1. already formed names are analyzed and their compatibility with the demands of the principles is confirmed, 2. already formed terms are analyzed, their form is examined following the basic terminology principles, with a new term being proposed with valid reasons, and 3. new terms are created according to the principles of term creation, where principles' application, hierarchy, and possibilities of combining are problematized. This paper aims to achieve three different goals. The first one is to present and review the current state of the terminology of theory of conceptual integration and its disarray. The arranged terminology would enable clarity and simpler understanding, which could consequently make it possible to systematically study and teach the theory itself. Furthermore, with elaborated and defined terms in the Croatian language, the theory of conceptual integration can be included in the study of the Croatian language and literature in parallel with the theory of conceptual metaphor as a part of lexicology or cognitive linguistics. All mentioned facts, if achieved, could enable the involvement of the Croatian linguists, their contribution to the theory, and their participation in international scientific communication. The second goal is to suggest the Croatian equivalents for all English terms, to suggest how to solve the existing problems with the disarrayed state of the terminology of the theory of conceptual integration, and to systematize the terminology of that theory. The third goal is to point to a problem of the hierarchy of terminology principles, i. e. questions which principle should when and in which case have an advantage over another and whether there is a possibility to even or combine the seemingly irreconcilable terminology principles. After the introduction, in which all the points above are mentioned, the second part of the paper covers both theories – the theory of conceptual metaphor and the theory of conceptual integration. Both of them, with the theory of conceptual integration being elaborated more extensively, are covered with examples in English as well as Croatian languages to explain easily the creating of terms. In addition, the basic terms of terminology, terminology principles, and the principles of creating a definition follow. The term terminology is polysemantic in Croatian language, which is in contradiction with one of the terminology principles which suggests that all terms in a field’s theory should be monosemantic. The term terminology can refer to a group of field’s terms and the science that deals with terms. To build crystal and systematized theoretical foundations of the paper, the term terminology is used to refer to the science which deals with terms, and the term nazivlje, which could be translated in English as nomenclature, to refer to the group of field’s terms. Making a difference between these two terms reduces the load of terms in Croatian language and the possibility of the creation of misunderstandings or errors. With the nine basic terminology principles, which all should be taken into consideration when creating a term, the definition of the term should follow. The definition should describe the meaning of an object with other known objects which enables its differentiation from other objects, that is – to determine the object, to establish the term and to differentiate the spoken object from the related ones, as well as to set them in interrelations. When creating a definition of the term, ten basic defining principles should be followed. Since most of the terms in English literature are descriptively defined, this paper brings the definitions created by following defining principles, and if the definition following defining principles already exists, the source is credited in the paper. In the third part of the paper, the terminology principles are applied to create the terminology of the theory of conceptual integration. Firstly, the terminology principles were applied to already existing terms which were found and taken from literature about the theory of conceptual integration in Croatian language to assess their position in the terminology of the theory of conceptual integration. After confirming the position of already created terms by applying the terminology principles and deducing whether they follow the principles, secondly, the alternation of one term is suggested for valid reasons. Thirdly, the terms which were, until now, not mentioned at all or used in English, were formed, and defined following both sets of principles. Croatian terms with their matching terms in English are listed in three different tables depending on whether they were confirmed, suggested to change, or only newly formed along with their definitions, which results in creating the preposition of Croatian terminology of theory of conceptual integration. The Croatian terms of the theory of conceptual integration were formed by the application of basic terminology principles in two different ways. In some examples, the term was formed following all terminology principles where neither of the principles interfered with another and all of them were completing each other, thus making a suggestion of a term more solid. In other examples, when forming a term, one principle was interfering with another and there was a necessity to determine to which principle, when, and in which situation should be given a preference to form a term. It is not disputed that the terminology principles should be mechanically followed, but in those examples, there has been a tendency to take the most, if not all, terminology principles into account or to combine them. With this paper the current state of the Croatian terminology of the theory of conceptual integration has been presented. Its current state could be described as disordered and inconsistent – some of the terms are formed in Croatian language, some are used in the original English form, others are not mentioned at all, and most of them are not defined as they should be. When taking into a consideration that the creation of the terminology in mother tongue is a challenging task, in which one terminology principle can interfere with another, it is not surprising to take an easier way out and combine both English and Croatian terms. If one terminology principle interferes with another, it is necessary to evaluate and establish a hierarchy of terminology principles and try to take into consideration as many terminology principles as possible with the aim to even or combine them. By choosing the more difficult path, this paper brings the systematized Croatian terminology of theory of conceptual integration which enables clearer and simpler understanding of objects, which this young branch of cognitive linguistics makes more available to linguists, students, and other interested researchers of language and human mind.