Politeness is considered one of the main principles of successful and socially acceptable communication. As a pragmatic term politeness is seen as a specific form of linguistic behaviour motivated by the intention of maintaining good relations with people. One of the most influential theories on politeness is the theory developed by Penelope Brown and Stephen C. Levinson (1987), who associate politeness with the speaker’s effort to avoid or mitigate the acts that potentially threaten the hearer’s or his own face, that is, their public self-image. The mitigation of face-threatening acts is done through a range of verbal and nonverbal strategies, which are aimed at attending either the hearer’s positive face, primarily associated with the desire to be approved of (positive politeness strategies), or the hearer’s negative face, primarily associated with the desire to be unimpeded in his actions (negative politeness strategies). According to Brown and Levinson, a face-threatening act can be done in four ways: 1) baldly on record, i.e. without redressing the act by minimizing the face threat, 2) by redressing the act with positive politeness strategies, 3) by redressing the act with negative politeness strategies and 4) off record, i.e. by using an utterance whose meaning is ambiguous and which can be interpreted as a non-threatening act (Brown, Levinson 1987: 68–70). Relying primarily on Brown and Levinson’s theory of politeness, but also applying some methods from other approaches (Leech 1983; 2014), this thesis examines the way in which politeness is realized in written business communication between native speakers of Croatian on the one hand and between non-native speakers of English, who use English as lingua franca on the other hand. Politeness strategies in Croatian and English business letters are examined through quantitative and qualitative corpus analysis. The corpus of 60 Croatian business letters and 60 English business letters has been collected and classified by language as well as by their illocutionary function, which determines the frequency and type of politeness strategies used. Each group of letters is analysed quantitatively with respect to two aspects: 1) to examine the frequency of politeness strategies in each group by determining the ratio of the utterances that contain politeness strategies to those produced baldly on record, i.e. without any strategies and 2) to examine the relation of positive and negative politeness in each group by counting the total number of politeness strategies and determining the ratio of positive politeness strategies to negative politeness strategies. The off-record type of politeness is not included since it is not applicable to this type of discourse. The qualitative analysis included the classification of the politeness strategies realizations in Croatian and English letters according to Brown and Levinson’s typology of positive and negative politeness strategies. Its aim was to examine linguistic means that are typically used in written business discourse to realize certain types of positive and negative strategies. The results of the quantitative analysis are compared between different types of letters and between the Croatian and the English corpus. They show that in both the Croatian and English corpus the use of politeness strategies is most frequent in competitive letters, which contain face-threatening acts but also aim at maintaining good relations with the receiver, such as requests, apology letters, letters with bad news etc. Second by the frequency of politeness strategies is the category of hybrid letters such as offers, enquiries and orders, which have a complex illocutionary function that at the same time threatens the receiver’s face and attends to it. It is followed by the category of conflictive letters, whose main function is to express the negative attitude towards the receiver (e.g. letters of complaint or warning), and the category of convivial letters, whose main function is to attend to the receiver’s positive face (e.g. invitations or letters with good news). The use of politeness strategies is the least frequent in collaborative letters, such as notices, whose main purpose is to inform and which generally do not contain threats to the receiver’s face. The results also show that English letters generally use more politeness strategies than Croatian letters and that the percentage of positive strategies in English letters is generally higher than in Croatian letters. The higher frequency of strategy use in English letters indicates that English letters pay more attention to politeness, i.e. maintaining good relations with the recipient at the expense of being direct and straightforward, while Croatian letters give higher priority to the efficiency of communication, which involves using fewer politeness strategies. On the other hand, the higher percentage of positive strategies in English business letters indicates that English letters are more prone to lowering the level of formality and creating more friendly and personal relationship towards the recipient. The qualitative analysis showed which subcategories of Brown and Levinson’s classification of positive and negative politeness strategies are applicable, appropriate and most typical in business discourse and how they are linguistically realized in Croatian and English business letters. For example, one of the most characteristic negative politeness strategies is dissociating the sender and the receiver from a face-threatening act by using impersonalized and passive sentences and by expressing the action associated with a face-threatening act through nominalization. However, some of those strategies are more conventionalized in one language than in the other, which means that in one of the languages they are usually realized through formulaic expressions which became a typical element of the business writing style, while in the other language they are performed through more original utterances. The thesis therefore observed the main principles of politeness by examining how they operate in written business discourse in comparison to other types of discourse, as well as comparing how they are applied in two significantly different linguistic and cultural surroundings. The similarities in the use of politeness between the two languages and with other types of discourse can serve as an insight into the universal principles of politeness and their applicability to different domains of interaction, while the distinctions in the frequency and the realizations of politeness in Croatian and English business letters indicate the aspects of politeness phenomenon that are culture-specific, language-specific or discourse-specific.