本文係在臺灣的歷史發展脈絡下，試圖解答「什麼是客家」的問題。針對這個問題，最簡單的回答是：客家是一個方言群或文化群的名稱，而在臺灣，客家也是一個族群的名稱。然而，客家卻不是臺灣歷史上固有的名稱，也不是一個自臺灣民間社會自然孕育而成的自稱或他稱，而是一個不折不扣的外來詞。儘管客家已成為今日國家制度上的一個正式族群名稱，但對這個外來詞被引進臺灣，並為臺灣社會所接受的來龍去脈，至今尚乏令人滿意的答案。既然客家是一個方言類別，方言又是客家文化的最大特徵，也是人群識別最為顯著的標記，更是結構臺灣傳統社會地緣和血緣之外的關鍵要素。因此，為了彌補以往研究之不足，從方言的角度入手，考察臺灣歷史上這個方言群的真正名稱，或許有助於從根本上釐清銜接戰後臺灣客家（Hakka）名稱的歷史演變圖像。全文除回顧相關研究主題外，主要是從分類學、發生學與地域社會的角度，並依據國家制度、西人書寫與民間口語等三個面向，分別探討臺灣自清代，經日治到民國時代，從「客家」（本貫主義）到客家（方言主義稱為的發展過程。然而，由於篇幅較長，乃分為上、下兩篇；上篇以探討國家制度和西人書寫的稱謂為主，而下篇則以民間口語的稱謂為重點。

This paper attempts to answer the question ＂what is Hakka?＂ in the context of the history of Taiwan. The most straightforward answer is that the term Hakka generally refers to a language or cultural group but also signifies an ethnic community in Taiwan. Nevertheless, the term Hakka did not stem from Taiwanese society and is a relatively recent addition to the history of Taiwan. It is a term of purely foreign origin. Although the term Hakka has been institutionalized as a formal ethnonym, how the term was originally introduced to Taiwan and utilized by the Taiwanese still lacks a conclusive answer. As language itself is the most significant feature of Hakka, in addition to other aspects such as territorial and kinship ties, this paper examines the real linguanym of what has come to be known as Hakka within the context of the history of Taiwan in order to comprehend how this said group obtained the name of Hakka in postwar Taiwan. The paper approaches the Hakka issue mainly from the perspectives of taxonomy, genesis, and territorial society, exploring the process from the＂Guest＂ (the principle of Bon-gwan) to the Hakka (the principle of vernacular language). Section One investigates the influence of the state institution and Western construction. Section Two discusses the labels adopted by the folk society.