R. Maslin progress has been achieved in the field of ceramic fibers. Quasi-stoichiometric SiC fibers display a higher thermal stability than the Si-C-O fibers. Hence, they are ompatible with high temperature processing techniques. However, their cost is too high and their stiffness (a 400 GPa) might be a problem for the fabrication of nD preforms. Si-B-C-N fibers, thermally stable and creep resistant, also appear to be attractive materials The key point in terms of material design is probably to improve the lifetime of CMCs in oxidizing atmospheres, via innovative interphase and matrix materials and concepts. A first approach has been to replace the carbon interphase by less oxidation prone materials. However, the most promising of them, BN, is usually moisture sensitive when deposited at low temperatures. A second approach has been the use of multilayered interphases. Its success lies in the fact that such interphases can be widely tailored, permitting the decoupling of some of the contradictory phase functions. The extension of this approach to the matrix itself also appears promising, at least when applied to composites processed via CVI-processes e In terms of processing, rapid densification techniques with processing times of e order of the day, are emerging beside well established routes(I-CVI. PIP. SIHP techniques) which could still be improved. Even if they display less flexibility, they may be appropriate for specific matrix compositions(the DIMOX process for alumina or the SILCOMP process for SiC)or specific applications Acknowledgements The author is indebted to his coworkers from LCTS, and more particularly Pailler, F. Langlais, X. Bourrat and C. Robin-Brosse, as well as to S. Goujard from sep division de snecma. for valuable discussion. He also acknowledges the assistance of J. Forget, F. Croizer and M. Saux for the preparation of the manuscript REFERENCES L. R. Naslain, The concept of layered interphase in SiC/SiC, Ceram. Trans. 58, 23-39(1995) 2. R. Naslain, Ceramic matrix composites: state of the art and future directions. in: Proc. Sth Japan Int. SAMPE Symp. (JISSE-5), Y Miyano and M. Yamabe(Eds). pp 7-12. Japan Chapte SAMPE, Yokohama(1997) 3. T Mah, N. L. Hecht, D. E. McCullum. J. R. Hoenigman, K. M. Kim, H M.Katz and H. A Lipsitt. Thermal stability of SiC fibres( Nicalon).J. Mater Sci. 19. 1191-1201(1984) 4. T J. Clark, R. M. Arons, J. B. Stamatoff and J. Rabe, Thermal degradation of Nicalon SiC tibers Ceram. Eng. Sci. Proe. 6. 576-588(1995 5.S. M. Johnson, R D, Brittain, R. H. Lamoreaux and D J Rowcliffe Degradation mechanisms of silicon carbide fibers, J. Amer: Ceram. Soc. 71, C-132-C-135(1988 6. E. Bouillon, D. Mocaer, J, F villeneuve. R. Pailler. R. Naslain, M. Monthioux. A. Ober- C. Guimon and G. Pfister, Composition-microstructure-property relationships in ceramic monofilaments resulting from the pyrolysis of a polycarbosilane precursor at 800 to 1400C. J. Mater: Sci.26.1517-1530(1991) C. Vahlas, Thermal degradation of Nicalon and Tyranno fibers, Ceram. Trans. 46. 41-52(1994)