Bibliography

Top Resources:

Stanford Encyclopedia of Philosophy (Extensive empathy description)
    Measuring Empathy
"Despite its linguistic roots in ancient Greek, the concept of empathy is of recent intellectual heritage. Yet its history has been varied and colorful, a fact that is also mirrored in the multiplicity of definitions associated with the empathy concept in a number of different scientific and non-scientific discourses. In its philosophical heyday at the turn of the 19^th to the 20^th century, empathy had been hailed as the primary means for gaining knowledge of other minds and as the method uniquely suited for the human sciences, only to be almost entirely neglected philosophically for the rest of the century. Only recently have philosophers become again interested in empathy in light of the debate about our folk psychological mind reading capacities."

 

Empathy at Wikipedia (Extensive article on empathy)

1 Etymology

2 Theorists and their definitions

3 Contrast with other phenomena

    3.1 Perspective-taking

4 The development of empathy

5 Neurological basis

6 Lack of empathy

    6.1 Psychopathy

    6.2 Enjoyment of others' suffering

14 References

15 Books

etc,

Compassion & Empathy  at Greater Good Science Center Wiki
Annotated directory of Studies

Answers.com (Extensive empathy description)
   Psychoanalysis Dictionary
Many and extensive definitions. In other languages, sign language, etc. etc.

Dictionary of the History of Ideas (Extensive empathy description)
"Empathy is the idea that the vital properties which we experience in or attribute to any person or object outside ourselves are the projections of our own feelings and thoughts. The idea was first elaborated by Robert Vischer in Das optische Formgefühl (1872) as a psychological theory of art which asserts that because the dynamics of the formal relations in a work of art suggest muscular and emotional attitudes in a viewing subject, that subject experiences those feelings as qualities of the object. Aesthetic pleasure may thus be explained as objectified self-enjoyment in which subject and object are fused."

Swedish Empathy Center  (Many resources, bibliography, articles, etc)

Empathy An Introduction to Empathy 
"What is Empathy, Definition of Empathy and Sympathy, History of Empathy"

Re-examining empathy: a relational-feminist point of view.
"For thousands of years people have been aware of the concept of empathy. In ancient Greece, philosophers expressed their understanding of "empathy" by the word empatheria, which implies an active appreciation of another person's feeling experience (Astin, 1967). In 1910, British psychologist Edward Titchener translated the German word "Einfuhlung" into empathy, literally meaning "to feel oneself into" (Bohart & Greenberg, 1997). In the 1950s, American psychologist Carl Rogers highlighted the importance of empathy in his client-centered approach to working with people. His description of empathy was widely adopted by social workers, giving common voice to its meaning in professional literature. According to Rogers (1951),"

Empathy and its development
Editied By Nancy Eisenberg, Janet Strayer

Perspective Taking and Empathy
A course bibliography on empathy