The article considers the special legal nature of parliament as a legislative and representative body of the state power. Attention is paid to such features as passing an act, availability of power, permanent action, collective nature of decision making, special orientation of powers, formation by electing. The author emphasizes the inadmissibility of equating between representative relations in parliament and lobbying, representation in the civil law and functioning of the elected individual authorities. The author offers the variant to differentiate the terms “parliament” and “parliamentarism”. Correspondingly, parliamentarism in constitutional law is offered to understand as a theoretical concept, a legal institution, a principle of government, and a special system of organization of state power, reflecting the significant role of Parliament in a particular state in practice. It is concluded that formation of parliamentarism, in addition to the functioning of parliament, requires the supremacy of law; separation of powers with clearly defined and real authority of parliament; parliament’s involvement in the formation of other branches of government; the accountability of the Executive Power to parliament; the special status of the deputy of the free mandate and responsibility before the law; the multiparty system; the independence of the judiciary.