[3] In 1951, Yeshiva University's Samuel Belkin encouraged Tendler to lead the Great Neck Synagogue for one year as an intern, thereby becoming the community's first rabbi.

[7][8] Tendler advocated the theory that complete and irreversible cessation of function of the entire brain renders a person "physiologically decapitated", and they are thus considered legally dead according to Jewish law.

[9] Tendler also asserted that once organ donation has been deemed permissible under the given conditions, it is indeed mandatory, falling under the rubric of the legal obligation of Jews to preserve the lives of others.

[10] In addition, Tendler has written extensively on euthanasia, infertility, end of life issues, organ donation, and brit milah (Jewish circumcision).

[11] Serving on an RCA panel on stem cell research, Tendler expressed respectful disagreement with the Bush administration's position.

[15] Tendler was responsible for the fact that modern-day Orthodox Jews in the United States and Israel generally do not consider swordfish to be a kosher fish.