Kesalahan atau kesulitan belajar bisa menjadi sumber penting dalam pembelajaran. Terdapat beberapa jenis kesulitan belajar aljabar yang dialami siswa, yaitu: (a) kesalahan dalam memahami lambang =; (2) tendensi penggunaan prosedur aritmatika dan pengabaian variabel; (3) generalisasi; (4) abstraksi; dan (5) pemaknaan grafik. Dengan mengetahui jenis kesulitan belajar tersebut maka guru bisa merancang pembelajaran yang tepat. Lebih lanjut lagi, jika merujuk pada pendidikan matematika realistik, terdapat empat pandangan tentang belajar aljabar, yaitu: (1) aljabar sebagai aktivitas manusia (algebra as human activity); (2) aljabar sebagai aktivitas otak (algebra as brain activity); (3) aljabar sebagai aktivitas personal (algebra as personal activity); dan (4) aljabar sebagai aktivitas yang bermakna (algebra as meaningful activity). Kata kunci: kesulitan belajar aljabar, pembelajaran aljabar Errors or difficulties in learning could be an important source of learning. There are several types of students difficulties in learning algebra, namely: (1) Errors in understanding the symbol =; (2) Tendency to use arithmetic procedures and to ignore variables; (3) Generalization; (4) Abstraction; and (5) Graph interpretation. Teacher can design appropriate learning by identifying those students difficulties. Furthermore, there are four views about learning algebra referring to Realistic Mathematics Education: 1) algebra as human activity; (2) algebra as brain activity; (3) algebra as personal activity; (4) algebra as meaningful activity. Keywords: difficulties in learning algebra, algebra learning.