Single-mode fiber splicing requires quite a precise core alignment for the adjustment of core eccentricity and outer diameter discrepancies. Several core alignment methods have been developed. The typical four methods are as follows: 1) remote injection and remote detection systems (RIRDS), 2) remote injection and local detection systems (LDS), 3) local injection and detection systems (LIDS), 4) core direct monitoring systems. The so-called prefusion method has been developed to prevent bubble growth during the fusion process. This method is widely used for both single and multimode fiber arc fusion splicing machines. The average splicing losses of 0.11 dB and 0.10 dB are reported for single-mode fiber splicings with RIRDS by NTT in Japan, and by Bell-Northern Research in Canada, respectively. With the LIDS method, the average splicing loss of 0.13 dB in the field was reported by PTT in The Netherlands. With the core direct monitoring method, average splicing loss of 0.08 dB in the field was reported by NTT in Japan. This method is one of the simplest on the most useful core alignment for single-mode splicing machine. Splicing of multimode fiber does not require a precise core alignment; that is, the alignment by the cladding is sufficient for the low-loss splicing. Therefore, the mechanism for the alignment of the fibers is much simpler than that of single-mode fibers. The average splicing loss of 0.07 dB was reported by NTT in Japan in 1982. As mentioned above, this paper reviews the field experience with these different splicing methods.