negative permeabilty and neagative permitivity

hi there
i am trying to learn about metamaterials. i just started.
i would like to know what exactly negative permeability and negative permitivity implies?
if any one could explain then please tell me what it implies in terms of EM waves and if possible some physical interpretation would be very helpful.

thanks.

Read:

Veselago's paper from the 1960s in Soviet Physics Usbekhi (sp)

Pendry's paper from ~2001 "Negative refraction makes a perfect lens"

Any of the papers in Science from D.R. Smith and/or J.B. Pendry and/or X. Zhang since 2000 including especially:

-the 2006 cloaking paper
-the ~2006 Controlling Electromagnetic Fields paper with Schurig
-the ~2000-2001 paper demonstrating negative refraction
-the ~2005 Zhang paper demonstrating a superlens
-the Zhang paper demonstrating an acoustic hyperlens

These are some of the seminal papers in both theory and experimental realization. Big groups include D.R. Smith at Duke, D. Schurig at NC State, N. Engheta at U Penn, X. Zhang at Berkeley, J.B. Pendry at ICL (Imperial College London), W. Padilla at BC, R. Ziolkowski at U Arizona. Many/most of the seminal papers discussing implications have come from these groups.