Party statutes formerly stipulated that congresses would be held every four years, but a decision was made to extend the interval to five years after the Communist Party of the Soviet Union had made the same change. Decisions of the congresses appear as party statutes that usually reflect the desires of the leadership and the circumstances that necessitated the additions, deletions, or amendments to already existing statutes. The most important innovations embodied in BKP statutes emerged from congresses beginning with the Sixth Party Congress, held in 1954, and continuing through the Tenth Party Congress, held in 1971.

The Sixth Party Congress abolished the position of general secretary and in its place created the post of first secretary, again following the lead of the Soviet party, which had done the same thing after Stalin's death a year earlier. Party leader Chervenkov, who was premier and a Politburo member, kept those posts and allowed the election of Zhivkov as first secretary. Zhivkov was then an unknown functionary who had risen from the ranks of the Sofia party structure. Aside from the usual exhortation for party unity and the changes in six Politburo positions as well as an increase in Central Committee membership, the Sixth Party Congress was uneventful. Zhivkov's rise to power did not take place immediately, and a period of intraparty struggle ensued as he gradually consolidated his authority as first secretary.

The Seventh Party Congress, held in June 1958, proved even more uneventful. It passed the Third Five-Year Plan for the development of the economy, the fulfillment of which was drastically reduced to three years even before the ink was dry on the document. With Central Committee approval, new plans for economic targets were prepared; meanwhile, Zhivkov prepared an elaborate propaganda campaign to push this program through. Zhivkov's Theses, as the collection of instructions have come to be known, advocated increased cultivation and production in agriculture and industry to obtain yields that were double those of previous plans. An unprecedented flurry of activity followed on the heels of extensive media coverage. Aided by the press, the Agitation and Propaganda Department under the Central Committee's direct supervision launched a vast campaign that surpassed even those efforts in neighboring countries.

This period is characteristically known as Bulgaria's Great Leap Forward, patterned after the Chinese experience, and historians put forth political and economic motives for such an economic experiment. Politically, after Nikita Khrushchev started his de-Stalinization policy in the Soviet Union, the Bulgarian repercussion was evident in Chervenkov's disenchantment with the Soviet trauma and his looking favorably instead toward the Chinese example. The Great Leap Forward was neither a spectacular success nor a dismal failure and achieved no more than the expected progress in three year's time. The ensuing period marked a return to earlier patterns and heralded the end of Chervenkov's political career and the concurrent elevation of Zhivkov. The election of Zhivkov's friends—Stanko Todorov and Mitko Grigorov—to full membership in the Politburo gave him added support. Khrushchev's visit as the head of a large Soviet government delegation did not hurt Zhivkov but rather gave convincing proof of Khrushchev's support of the Bulgarian first secretary. Anton Yugov was premier at this time, but it was not long before he too was purged, the final blow coming only hours before the start of the Eighth Party Congress.

The Eighth Party Congress in 1962 marked the end of the open opposition to Zhivkov's leadership. With Chervenkov and Yugov out, Zhivkov was in full control. A month earlier, in October 1962, a special plenum of the Central Committee announced Zhivkov's assumption of government power as premier while retaining the first secretaryship of the party. In the economic sector, the Twenty-Year Plan of Economic Development—patterned on that of the Soviet Union—had been passed. It featured more realistic goals in contradistinction to its predecessor. As usual, heavy industrial priorities ranked high in the development plan.

In November 1966 the Ninth Party Congress was held in Sofia. During the deliberations changes were made within the Politburo whereby Zhivkov's former protégé, Grigorov, was dropped from membership without an explanation and Todor Pavlov, a theoretician of Marxism, and Tsola Dragoycheva, head of the National Council of the Fatherland Front, were added as full members. Boyan Bulgaranov and Ivan Mihailov, both older party members, were retained—a move that indicated the influence of older functionaries over young potential leaders. Economically, the congress supported principles of new management, tying political progress with economic advancement.

Collectively the aforementioned congresses accomplished little. On the contrary the 1971 congress introduced considerable changes in the sociopolitical and socioeconomic patterns of growth—among them the drafting and adoption of a new constitution (see ch. 8).

Tenth Party Congress

Whatever political changes are visible in Bulgaria are the result of the Tenth Party Congress held in Sofia from April 20 to April 24, 1971. It was attended by 1,553 delegates representing roughly 700,000 party members, a ratio of about one delegate for every 450 members. Additionally, foreign representatives from eighty-nine countries were on hand. Leading the Soviet delegation were Brezhnev, general secretary of the Soviet party, and four other high-ranking officials.

As is customary, Zhivkov opened the congress with his usual state-of-the-nation address, extolling Bulgarian-Soviet ties and stressing friendship between the two countries. Included in the agenda were the adoption of a new five-year economic plan; discussion and adoption of the new party program; discussion and approval of the new constitution; the election of party members to the Central Committee, Politburo, and Secretariat; and a change in party statutes calling for a congress every five years instead of four.