بعثیسم یا بعث‌گرایی (به عربی: الْبَعْثِيَّة)، به ایدئولوژی حزب بعث گفته می‌شود که مشوق پان‌عربیسم و ایجاد کشور واحد عربی است. به‌طور خلاصه، بعثیسم بر روی دو آرمان سوسیالیسم و ملی‌گرایی عربی تکیه دارد. گفتمان بعثیسم از درون بحرانی عمیق در جهان عرب پدید آمد که «چندپارگی اعراب»، «تسلط امپریالیسم اروپایی» و «فشار استبداد داخلی» سه ضلع این بحران را تشکیل می‌دادند. در چنین شرایطی، منطقی به نظر می‌رسید که حزب بعث گفتمان خود را پیرامون سه اصل اساسی «وحدت، آزادی، سوسیالیسم» (الوحده، الحریه، الاشتراکیه) طرح‌ریزی کند.[۱۶]
پس از انشقاق در حزب بعث، بعثیسم عراقی و سوری از هم فاصله گرفتند و پس از سرنگونی رژیم صدام در عراق و جنگ داخلی سوریه، این حزب در ضعیف‌ترین حالت خود قرار گرفت و درنهایت، پس از سقوط رژیم اسد در سوریه، این ایدئولوژی سیاسی به تاریخ سپرده شد. با سرنگونی رژیم صدام، برخی از بعثی‌های عراقی با گروه‌های تندرو و سلفی داخل عراق، هم‌پیمان شدند. اسناد به‌دست آمده از داعش نشان می‌دهد مغز متفکّر و اجرایی تصرف موصل، تکریت و دیگر شهرها برخی افسران پیشین ارتش بعثی عراق بودند.[۱۷]
گفتمان بعثیسم بر سه اصل «وحدت عربی، آزادی و سوسیالیسم» استوار بود:
تسلط اندیشه‌های میشل عفلق که یک مسیحی ارتدوکس بود و رواج ملی‌گرایی و سوسیالیسم به عنوان «ایدئولوژی زمان» مانع از آن شد که هرگز اسلام به عنوان نقطهٔ مرکزی بعثیسم مطرح شود. به‌طور کل، دیدگاه بعثیسم نسبت به حکومت، دیدگاهی سکولار است و استفادهٔ افرادی چون صدام حسین از امتیاز اسلام، بیشتر استفاده‌ای ابزاری به منظور همراه کردن بیشتر اعراب است. در چنین گفتمانی، اسلام به عنوان امتیاز عرب بر غیرعرب تلقی می‌شود. از این منظر، اسلام یک جنبش عربی بود که مفهوم آن عبارت بود از تجدید حیات و تکامل عربیسم. در یک‌کلام، در ایدئولوژی بعث اسلام یک پدیدهٔ تمدّن عربی است.
Ba'athism as an expression of Arab nationalist identity had little patience for a political discourse limited by an attachment to a single faith system. For the founders of Ba'athism, the principles of secular, nationalist socialism would unite all Arabs irrespective of religion, nation or class.
Ba'athism is a mixture of pan-Arabism and Arab socialism. Its ideology laid down by the Ba'ath founder, Michel Aflaq, calls on a number of potentially incompatible and conflicting ideas. It is pan-Arabist in its aspirations yet appeals to individual nationalisms. It assumes the existence of an Arab nation and calls for the establishment of a single Arab state, but at the same time is used by its leaders in Syria and Iraq as a powerful mechanism for establishing the power and legitimacy of those states. It appeals to Islamic religious principles and the traditions of Arab history whilst at the same time aspiring to create a secular modernity, which it recognises as the basis of western prosperity and power. The socialist dimension of Ba'athism is reflected in its claim to eliminate the conflict between the different ethnic groups found in Middle Eastern countries, thus denying the monopoly of power to any one group. In practice, particularly under the rule of Saddam Hussein, it has on the contrary resulted in the concentration of power into the hands of a small clique, many of the members of which have family connections. From an international perspective Ba'athism's socialist aspirations entail the rejection of liberal economics based upon capitalistic principles and, at least in Cold War terms, it saw the Soviet Union as its natural major supporter in its stand against what it conceives to be western imperialist influence and intervention in the Middle East.
The Ba'ath ideology was comprised of rigid systems of beliefs, with the idea of Arab unity as the main core. Ba'athists believed that they should use all means, including coercive measures, to achieve this goal.
Ba'athism is a revolutionary philosophy whose technique has been to foster and lead revolution from below—the very fragmentation of many Islamic societies precludes sufficient solidarity at the grass-roots to make a general uprising a viable strategy. The method is to capture power by whatever means possible and institute the revolution from above.
Ba'athism emerged as part of a global efflorescence of populist, socialist, and other anti-systemic movements encompassing the 1917–1973 wave of national revolts which went by various names, including the anticolonial movements or the emergence of the South... Forces of socialism, communism, and left-wing Ba'athism were increasingly setting the agenda within Syria.
The Baath was the most ardently Pan-Arabist movement of all; its program combined a secularist worldview, populism, a vaguely Marxist socioeconomic program, and a visionary dream of a single Arab nation stretching from Morocco to Iraq.
For the Party to succeed in achieving these aims, Aflaq insisted that the Baath had to be nationalist, populist, socialist and revolutionary. The radicalism of the Baath later became more manifest as a result of the Sixth National Congress held in Damascus in October 1963. The Congress declared the peasants and workers to constitute the base not only of the 'Arab revolution' but also, and more significantly, of the Party itself. Accordingly, only peasants, workers and revolutionary intellectuals of civilian or military background could accomplish the socialist revolution. Moreover, the Congress insisted on the need for workers' control of the means of production, and for an agrarian reform where collective farms would be governed by peasants.
The traditional Gulf states now represented by the GCC have accordingly grave concerns for the security of their monarchist regimes from republican radicalism on the left as represented by Iraqi Ba'athism or South Yemeni Marxism or republican radicalism on the right as represented by religious fundamentalism.
Ba'athism is not democracy, but it is indissolubly linked to a republican form of government.
Ba'athism and most other Arab nationalist movements drew on the widespread anti-colonial themes as well as on hostility toward Israel, which became associated with colonialism in pan-Arab discourse.
Ba'athism espouses, at least in theory, non-alignment, pan-Arabism and anti-imperialism (in practice, Ba'athists aligned themselves with the Soviet Union during the cold war).