A novel domain for Index Modulation (IM) named "Filter Domain" is proposed. This new domain generalizes many existing modulations and IM domains. In addition, a novel scheme "Filter Shape Index Modulation" (FSIM) is proposed. This FSIM scheme allows a higher Spectral Efficiency (SE) gain than the time and frequency IM dimensions in Single-Input Single-Output (SISO) systems. In the FSIM system, the bitstream is mapped using an Amplitude Phase Modulation (APM) as QAM or PSK, and an index of a filter-shape c hanging a t the symbol rate. This filter s hape, b eing c hanged a t e ach symbol, enables a SE gain in SISO system without sacrificing a ny time or frequency resources. Compared to an equivalent 8QAM and 16QAM schemes and at the same SE, the FSIM with QPSK using 2 and 4 non-optimal filter s hapes a chieves a g ain o f 3.8 dB and 1.7 dB respectively at BER= 10 −4 , and this superiority is maintained in frequency selective fading channel compared to equivalent SISO-IM schemes. A low complexity detection scheme, approaching the maximum likelihood detector performance, is proposed along with a full performance characterization in terms of theoretical probability of filter i ndex e rror a nd B ER lower bound. Finally, FSIM can achieve better spectral and energy efficiencies w hen a fi lter ba nk an d an IS I ca ncellation technique are optimally designed.