We had to do this. Erin slept through the night beautifully from 6 weeks old to 16 weeks old when we moved house. From 16 weeks she would wake up sporadically & need cuddles to go back to sleep.
We established that she wasn't hungry & it got so bad that OH was sleeping in the spare room to get some sleep. Erin was still in with us.
By 6 months, I had had enough - we'd tried moving her into a bigger cot in case it was a space issue, had tried tiring her out during the day - no use. And because she woke up at any time, with no routine, it was shattering.
Eventually we discussed it between us and decided to try controlled checking. It's something we'd introduced for her daytime naps with great success, so wondered how she'd be at night.
The first night I settled her as normal, with breast-feeding, but when she woke up, she took an hour & 20 minutes to settle at about half 11, but when she woke up again at 4, I automatically took her out & fed her without thinking.
The second night she took 20 minutes to settle herself to sleep initially, and woke up once that night which took 20 minutes again to settle her.
The third night she settled herself within 5 minutes upon going to bed and although she grimbled at about half 2, she didn't wake up and since then she's slept through again, unless poorly.
The first night was hard, with going to her after 1m, 2m, 3m, 4m, 5m, 6m etc and getting to 10m and not wanting to leave her any longer than that whilst crying, so then every 10m going to her, patting her back and saying "shhh, mummy's here, it's all right" or something like that.
In hindsight, it was probably a bad decision to get *me* doing this as she could smell the milk which probably prolonged the crying. I don't know...
It is hard, but perseverance and a commitment from the both of us helped. Steve was texting me from the spare room to make sure I was ok as he didn't want to come in and disturb what was going on.