Encyclopedia of Jewish Concepts - Philip Birnbaum, p. 92
The term Noachians (Bnei Noach) denotes all the descendants of Noach, who survived the Flood along with his closest kin.  The seven Noachian precepts, distinct from the laws obligatory on the people of Yisrael alone, are binding on all human beings.  They prohibit:
  1. Idolatry
  2. murder
  3. theft
  4. blasphemy
  5. incest
  6. eating the flesh of a living animal
  7. promotion of justice
All non-Jews who observe these laws, upon which all civilized society depends, are deemed worthy of life in the world to come.
The prohibition of cruelty to animals is reminiscent of biblical laws forbidding plowing with a mixed team of an ox and a donkey or taking a mother bird and her young from the next at the same time or muzzling an animal during the threshing season or slaughtering a cow and her calf on the same day (Devarim 20:10; 22:6; 25:4; VaYikra 22:28).  Man's obligation not to inflict cruelty upon animals is rooted in the recognition that they represent the handiwork of the Creator.
The talmudic statement concerning the seven Noachide precepts reads:   
Sanhedrin 56a
Our Rabbis taught: seven precepts were the sons of Noach commanded: social laws (I.e., to establish courts of justice, or, perhaps, to observe social justice (Nachmanides on Bereishit 34:13): Hast. Dict. (s.v. Noachian precepts) translates ‘obedience to authority’; to refrain from blasphemy, idolatry; adultery; bloodshed; robbery; and eating flesh cut from a living animal (These commandments may be regarded as the foundations of all human and moral progress. Judaism has both a national and a universal outlook in life. In the former sense it is particularistic, setting up a people distinct and separate from others by its peculiar religious law. But in the latter, it recognizes that moral progress and its concomitant Divine love and approval are the privilege and obligation of all mankind. And hence the Talmud lays down the seven Noachian precepts, by the observance of which all mankind may attain spiritual perfection, and without which moral death must inevitably ensue. That perhaps is the idea underlying the assertion (passim) that a heathen is liable to death for the neglect of any of these. The last mentioned is particularly instructive as showing the great importance attached to the humane treatment of animals; so much so, that it is declared to be fundamental to human righteousness).
By observing these as a minimum, a non-Jew settling among Jews might enjoy the privileges and responsibilities of a full-fledged proselyte.  Hence, there is no imperative need for a non-Jew to adopt the Jewish faith in order to merit salvation.
The attitude of Judaism to conversions i based on the conception of the seven precepts that were imposed on the descendants of Noach, or the entire human species.  "Judaism was a missionary religion, but its missionary activity was of a restricted character.  No organized attempt was made by official Judaism to propagate the observance of the practices of the Jewish religion which were never intended for any other people than Yisrael by virtue of her priestly calling.  All that Judaism was concerned with in its missionary work was to substitute the religion of humanity, communicated to Noach...  [Then] Judaism withdrew from the missionary field and was satisfied to leave the task of spreading the religion of humanity to her daughter faiths...[that] shared in common many truths, religious and moral, with the mother faith..." (Epstein, Judaism).
The Noachian precepts represents a theory of universal religion, emphasizing good actions rather than right belief, ethical living rather than credal adherence; they require only loyalty to a basic code of ethical conduct, and rest upon the recognition of a divine Creator.