The collection presented here contains papers delivered at the National Scientific Conference in memory of Prof. Yordan Zaimov, Ph.D. (1921–1987), on the occasion of the 80th anniversary of his birth, as well as several other texts. Through the conference and this collection, colleagues, students, friends, and admirers express their deep respect for Prof. Zaimov, their gratitude for his achievements, and their admiration for his selfless dedication to others.