Halacha, Jewish law, is one of the most important components of Judaism, but is often a matter of contention and difficult to define. The Reform Movement views Halacha as non-binding - something that is taken into account but is not mandatory. Both Orthodoxy and the Conservative/Masorti Movement, on the other hand, claim to be "halachic movements," although they often disagree as to what the Halacha is in a specific case, and even in the proper method for determining it. Furthermore, within each of these two movements, rabbis often disagree with each other about the Halacha. One will state that something is permitted; the other will proclaim it forbidden. Who is right? This may be the reason one is supposed to choose a rabbi and abide by whatever that rabbi says, instead of shopping around until you get the answer you want. Rabbi Joel Roth, one of the Conservative Movement's most distinguished halachists, has pointed out that we use Halacha in two ways: to signify the conclusion reached by a legal authority, a posek, on a specific matter, and to signify the process by which legal conclusions are reached. In this sense, the term refers to all of the factors that must or that might be considered by a posek before reaching his pesak (decision). When all of these factors are expounded together with the resultant norm, it rarely appears simple, clear or definitive. Rather, it is complex, ambiguous, and replete with grounds for disagreement among poskim (The Halachic Process). It is therefore strange to hear rabbis in high official positions stating that "the halacha never changes," as if all of the discussions and decision-making processes that we find recorded in the Mishna, the Talmud and the great works of poskim throughout the ages never took place! Of course Halacha changes, because different conclusions are reached by different authorities and because different circumstances call for different answers. Even when we say that all the Law - Written and Oral - was revealed at Mount Sinai, what we really mean is that the basis of all Jewish Law is found in the Torah and in the principles of interpretation that govern how that Torah is to be interpreted. The tradition itself has always recognized that the determination of Halacha rests upon the authority of the rabbis, and that it is determined by the majority. "It is not in heaven!" is the watchword. Rather, it is to be determined by human beings who are versed in the Halacha and who are seeking to determine how God's will can be realized - not by searching the heavens for supernatural signs but by studying the tradition and examining the needs of the time. Rabbi Emanuel Rackman, a highly respected Orthodox rabbi, has pointed out that in determining the Halacha, poskim have always taken into consideration "what practice has become widespread among Jews, what is required socially because of the precepts of peace, what will keep the world aright and many other social criteriaâ€¦ These standards are as much a part of Torah as the texts themselves" (One Man's Judaism). Were it not for the ability of Jewish law to adapt to new needs, we would have no synagogues, no rabbis, no ketubot, no conversions - none of which are to be found in the written Torah. Thus Halacha is essential to Judaism; it is the spine of the Jewish body politic. But Halacha is only as good as those who determine it. We need Halacha today that is rooted deeply in the Jewish tradition but that is also capable of understanding the times in which we live, the circumstances of our lives and the needs of the Jewish people. We need a Halacha that does not automatically say "anything new is forbidden by the Torah." It is always easy to say "no" in answer to a halachic question. It may be more difficult to say "yes," but often that is the true art of the halachist - to know how to find that which is permissible and not always to impose new prohibitions. In the words of the erudite Rabbi Louis Jacobs, "...the Halacha is a living corpus whose practitioners were far more than mere transmitters of a noble heritage. They were creative thinkers, responding both intellectually and emotionally to the challenges and needs of the age in which they lived, with their quota of human temperament and failings, as well as being highly gifted leaders who tried to pursue the truth objectively as a divinely ordained task" (A Tree of Life). If we are fortunate enough to be blessed with leaders of that sort today, the Halacha will once again become that which it was historically: the guide to living a life that is pleasing to God. The writer is the head of the Rabbinical Court of the Masorti Movement and the Rabbinical Assembly of Israel.