Q. What is the difference between the LL.B. degree and the J.D.degree?

A thorough and well-documented discussion of the distinction between the LL.B and J.D. degrees can be found in 72 LAW LIBRARY JOURNAL 153 (1979):

…the LL.B. "stands for 'Legum Baccalaureus,' the formal Latin designation for what was once almost universally the first professional law degree in the United States, the Bachelor of Laws.  The double 'L' is known as the reduplicative form of the plural..." and continues in modern usage ("pp" for pages, "JJ" for judges, etc).

The LL.B. degree was first awarded in this country in 1820 by Harvard and rapidly grew in acceptance as the standard first professional degree in law.  The propriety of awarding a bachelor's degree for legal studies could be traced to the fact that admittance to most nineteenth-century American law schools was predicated upon satisfactory completion of high school....

The history of the evolution of the J.D., or Juris Doctor, as a competing first professional degree spans most of this [20th] century.  The awarding of this degree was suggested by the Harvard law faculty in 1902 but their proposal did not meet with University approval.  In 1903, the University of Chicago Law School, which was one of five law schools then demanding a college degree from its applicants, conferred the J.D. on its graduates.  The editors of the HARVARD LAW REVIEW [18 Harv. L.R. 51 (1904)] agitated for a similar change at Harvard...but their cry went unheeded....

The modern trend toward acceptance of the J.D. had its impetus in a campaign by John G. Hervey, then dean of the Oklahoma City University School of Law.  The turning point appears to have occurred when the ABA Section of Legal Education and Admissions to the Bar unanimously adopted a resolution recommending to all approved law schools that they give favorable consideration to the conferring of the J.D. Degree as the first professional degree.  (This resolution is reprinted in full in the 1965 ABA REVIEW OF LEGAL EDUCATION 21)....

On April 7, 1969, the Harvard Corporation voted that the J.D. would thereafter be awarded as the first degree in law and that it would be made available retroactively upon application to recipients of the LL.B. degree of the Harvard Law School.

For additional information on the history of the Bachelor of Laws degree (LL.B.) at Harvard, see On the Battlefield of Merit: Harvard Law School, The First Century by Daniel R. Coquillette and Bruce A. Kimball.