Syntax: np.concatenate((a1, a2, ...), axis=0) a1, a2, ...: Sequence of arrays to join. axis: The axis along which the arrays will be joined. Default is 0. All arrays must have the same shape except in the dimension corresponding to axis. import numpy as np arr1 = np.array([1, 2]) arr2 = np.array([3, 4]) concat_arr = np.concatenate((arr1, arr2)) print(concat_arr) [1 2 3 4] import numpy as np a = np.array([[1, 2]]) b = np.array([[3, 4]]) concat_2d = np.concatenate((a, b), axis=0) print(concat_2d) [[1 2] [3 4]]